ST. LOUIS — In order to get something of value in a trade, one must present something of equal value. It's the oldest rule in business, and right now, one that may cripple the St. Louis Cardinals at the trade deadline in the coming weeks. 

The Cardinals sit at 45-45 after Saturday night's win over the Arizona Diamondbacks, but they haven't won more than three games in a row since the end of April, can't score runs and have far too many players under-performing. Worse, the players they do have who carry moderate trade value may not help their season or bring them a lot in return. 

When fans shout "SELL" on social media, I ask them what are they possibly selling right now? John Mozeliak would be the real estate agent standing outside an apartment building that looks nice from the outside, but is burnt to a crisp on the inside. You can't hide the smell of these 2019 Cardinals. 

RELATED: Cardinals place Molina on IL, activate Carpenter in roster moves before start of 2nd half

The president of baseball operations, aka the real general manager, has told the media over the past week that if a trade was going to be made, it would have to instantly improve the club or help their chances this season. He isn't going to make a trade to simply make a trade, like he did last season with Tommy Pham.

So, who are they moving and what can they get? Let's pop the hood and run diagnostics.

Matt Carpenter? Nope. He's stunk at the plate since early September, got an extension and will be 34 in November. He isn't even getting on base right now. No team is taking that on or giving much. 

Kolten Wong? He sure can pick it at second base, but what good is a .240's batting average, little pop and a career .705 OPS to a team? He currently holds a 1.1 fWAR. Wong will be 29 in October and next year his salary jumps from $6.5 million to $10.5 million. A team may take him, but they wouldn't give the Cardinals enough in return to justify the trade. 

Paul Goldschmidt? Shut up. 

Paul DeJong? Quite honestly one of the team's best trade pieces is also extremely vital to the team. There isn't a shortstop in the system who is ready to produce like DeJong, and no, Tommy Edman can't do it. DeJong has a plus bat with pop, has cut down on his strikeouts and already owns a f2.8 WAR this season. He's also signed through 2023 on the very modest contract holding an AAV of $4 million. Don't trade him. 

Yadier Molina? Shut up. 

Andrew Knizner? Shut up. 

RELATED: As Paul Goldschmidt goes, the Cardinals will follow in the second half

Marcell Ozuna? Assuming he makes a speedy and complete recovery from his broken fingers, Ozuna is the team's best trade piece. But what if he doesn't find his way back before July 31. What if he needs rehab? Will a team really pour a cup of expensive bourbon for a guy whose contract expires in months? What if he isn't the same hitter or goes into one of his slumps? So many questions. Ozuna is attractive to other teams, but how attractive? Without him, the offense has looked abysmal. 

Dexter Fowler? While he's recovered from a terrible 2018, his trade value still isn't good. He's getting on base, but not reinventing the way hitting is performed with a 107 wRC+ and overall fWAR of 1.2. There are two years left on that contract, and Fowler turns 34 before next season. The legs look better in the outfield, but I wouldn't get overzealous on a few good plays.

Harrison Bader? He saves runs in the field, but costs you runs at the plate. After a fine offensive season last year, Bader can't hit much this year, flirting with the Mendoza line and showing little power. He makes outstanding catches but can't hit at all right now. Will teams beg for that or give up big pieces in return? I doubt it. Like Wong, it makes more sense to keep Bader, send him to Memphis for retooling and see what happens. He's under team control until 2024. A cheap project. 

RELATED: Minor league team honoring jacked Cardinals outfielder Tyler O'Neill with 'bobble-bicep'

Jose Martinez? An AL team may bite, but the dilemma that applies to Bader and Wong comes into play here. Would your return for "Cafe" be worth the trade? He's got a two-year contract that is very team friendly. The time to trade the man was last year or the year before when he was a freak at the plate and rocking a 125-135 wRC+. Now, he's crashed back to Earth. Too late.

Tyler O'Neill? Oddly enough, the former Mariner has only played 91 MLB games. He's under control until 2025, and has power to go with a versatile skillset in the outfield. The strikeouts are there, but O'Neill may be an attractive piece to another team. At the same time, he's an unknown due to little playing time. You aren't getting a ton for him. Package Ozuna, O'Neill, and Wong together perhaps... unlikely. 

Jack Flaherty? Shut up. 

Dakota Hudson? An unwise move due to the age and still-budding ability, but definitely not a shut-up response. 

Daniel Ponce de Leon? Teams would take him right now, but aren't he and Hudson much more attractive to a Cards team seeing a regression in Miles Mikolas and losing Michael Wacha and Adam Wainwright next year? I'd said so. 

Wainwright? You wouldn't get much. He's effective, but also hurt every other 2-3 weeks. 

Mikolas? Play the lottery and you'll be more successful than finding a team to take that contract now. 

Carlos Martinez? This is an interesting situation solely based on the team's usage of the right-hander over the past year. He was once a promising starter, then a presumptive ace, and now he's a bullpen tool turned closer replacement. I'd say keep him. The $10 million AAV on a contract that has options running through 2023 still holds weight for the Cardinals. I still imagine a rotation next year with Martinez, Flaherty, Hudson, Reyes and Mikolas/Ponce. Having said that, if the team plans to waste his talent, trade him and get something while the iron is hot. 

Giovanny Gallegos? Shut up. 

John Brebbia and John Gant? Who replaces them? They are cheap, indispensable bullpen arms who provide a valuable service. You won't fix the offense by trading them, so hold onto them. 

Remember folks, you need to be able to replace what you sell. Why go out and acquire Will Smith if you are going to puncture the other part of your bullpen? If you sell DeJong, who plays short? If you trade Ozuna, is O'Neill starting every day in left? 

It's easy to say blow it up and sell it all. The Cardinals were supposed to be a playoff lock and currently sit as a team unlikely to even grab a wildcard spot. Unless the trade brings you future value, don't do it. 2019 won't be saved so easily. 

The Cardinals need their current roster to play to expectation, especially Goldschmidt, Carpenter and Mikolas. Three guys who I wasn't worried about in spring training are having bad seasons. If they wake up, the team will follow. 

That's a lot to ask but so is asking for a miracle in trades when every team knows the Cardinals are leaking oil.