It's going to be extremely difficult for anyone to know what rights (and remedies) you or the seller had under the contract between the two of you without reading the contract first. That said, this situation seems shady to me, and if I were you, I'd expect either my money back or the truck returned -- it seems wrong that the seller is keeping both.
If I were you, I'd contact a lemon lawyer, property lawyer, or contracts lawyer in St. Louis and have a chat. If the seller doesn't return your calls, I'm betting he returns the calls of a lawyer lickety split, especially if you have a case. Most here on avvo offer 30-minute consultations for free, so use the search feature and find one you like.
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