Let's do a little character evaluation on Jerry:
1. Jerry is shown to be spineless, inept and incompetent in pretty much everything he tries. He is basically a hapless loser who tries but just can't get anything done right. The Coen Brothers have described Jerry as an "amateur criminal". This is first evidenced in the scene where Jerry is finalizing a sale for a new car to a couple and the man is infuriated that Jerry added the $500 TruCoat onto the $19,500 car and charged him for it even though the man specifically stated he didn't want it. Instead of Jerry conceding and taking the cost off the man's bill, he says he'd go talk to his boss about it. However seeing as Jerry is the boss (he later tells Marge that he is the sales manager), we see that he steps into the break-room to talk to a co-worker to make it seem like he just spoke to "his boss". When he comes back,Jerry says he could get $100 knocked off the cost of the TruCoat, infuriating his customer even further.
2. We also see that Jerry's father-in-law Wade, who owns the car dealership Jerry works at, practically despises him and makes little effort to hide it. Wade does not like Jerry because he is aware of Jerry's craftiness or of the thought that Jerry may have married his daughter, Jean, just because he is wealthy, which is later shown that with the exception of his and Jean's son, Scott, Jerry shows little or no concern or affection for both his father-in-law or his own wife.
3. So we can assume Jerry was likely involved in some sort of business scheme or schemes where he lost a lot of money, because he apparently didn't know what he was himself getting into. It is speculated that sometime before the events in the film, he created fake invoices for vehicles he "sold" at the dealership even though they didn't actually exist.
4. Jerry sent the sold invoices along with a insurance loan request off to the dealership finance company with illegible VIN numbers... somehow hoping they wouldn't notice. The finance company, GMAC, calls Jerry at least twice on-camera to confront him about the accounting irregularities and wanted the VIN numbers as evidence of the sales or else they would pull the loans on the vehicles which total $320,000. The reasons for Jerry doing this remain unknown. Speculation from various viewers say that Jerry probably embezzled money from the dealership bank accounts and then borrowed the money from GMAC to replace the money he stole. Another speculation is that Jerry wanted the $320,000 loan to pay off other creditors he owes money too, or that he either spent or gambled the $320,000 loan away for personal use (though there is nothing in the film to suggest that Jerry has a gambling problem).
5. Clearly, Jerry knew that this plan only had a limited run so, through the association of a mechanic employee and ex-convict, Shep Proudfoot, Jerry meets and hires Grimsrud and Showalter to kidnap his wife in order to ask for a ransom of $80,000 from Jerry's father-in-law which Jerry will split with the kidnappers so Jerry could show as proof of car sales for GMAC. Though Jerry tries to call off the kidnapping at one point because he thinks that a real estate deal he brings to Wade's attention will get him out of the bind he is in financially. But Wade takes the deal solely for himself and offers Jerry a measly finder's fee. Jerry is too late to call off the kidnapping anyway and so Jerry tells Wade that the ransom is $1,000,000 (so that Jerry can use $320,000 of it to pay back GMAC when they demand their money back, and probably to spend the rest for personal use).
6. Through a course of events, which includes Grimsrud and Showalter shooting and killing a Minnesota State Police trooper who pulled them over for not having temporary vehicle tags on their car (followed by Grimsrud chasing down and shooting two passing motorists who see Showalter moving the trooper's body off the road), Showalter calls Jerry and says he wants the entire $80,000 ransom, leaving Jerry with nothing. Of course everyone knows that Jerry is in no position to negotiate, threaten or demand anything from Showalter and Grimsrud. Being inept and having poorly thought out of this kidnapping plan, Jerry doesn't have anything on the kidnappers to use for leverage, but they have everything on Jerry, as Grimsrud and Showalter know that Jerry personally met and hired them to kidnap his wife and if the police should capture them first, they can always rat on Jerry by claiming that he was the mastermind of this whole thing. Jerry knows that he has no choice but to agree to any demands the kidnappers threaten him with.
7. Once again, this plan backfires on Jerry because his father-in-law knows how unreliable Jerry is and doesn't trust him with the ransom money (rightfully so) and insists on going to the exchange himself. Jerry, being spineless and afraid of his father-in-law, does not insist on going in his place or even going with him, even though he also knows that Showalter is also very pissed off. For some reason, Jerry decides to go to the meeting anyways and he finds Wade's body, which he puts in his car trunk (and possibly he knows that Wade is dead as he's entering the parking garage, given that he passes a bloodied Carl going there). After this, Jerry goes back into work as if everything was hunky-dory until Marge goes back to interview him again. Jerry panics and flees the scene. He is eventually apprehended at a motel in North Dakota. As a final irony, Jerry, being incompetent to the end, uses the same 'Jerry Anderson' alias that he uses when checking into the Fargo, North Dakota inn where he first meets Grimsrund and Showalter.. thus enabling the police to easily track him down.