Exploits with Smart Contracts and Code Illiteracy

[Mendo Crypto]

I'm relatively new to blockchain technology so please cut me some slack, but what prevents sellers and resellers of ERC20 tokens via smart contract from stipulating some sort of hidden agreement that transfers the money back to the sender at a later time... so the recipient thinks everything is all good and doesn't realize the smart contract is still in effect and counting down to repay the "loan". How hard would it be to scam people in this particular way. It's sort of a variant on the double spending problem I suppose. Thoughts?

-R0BS0L33T