It took me forever to understand this about Bill Cipher, but when Mabel said he “makes bad deals,” she didn’t mean Bill’s a literal genie.

Bill makes deals that take advantage of the implicit trust that the deal’s being enforced. The fiery handshake thing is classic misdirection, an eye-catching gimmick that makes you think the deal is somehow magically official. It’s not. You only have Bill’s word that he’s going to follow through on something, and his word isn’t worth much.

People have tried to find some loophole in his deal with Dipper that allowed him to break the laptop–some kind of wordplay. It’s just not there. After Bill got what he wanted based on the flimsy exact-word premise of their agreement, he canceled their deal.

Bill tried to follow through on his deal with Gideon only because their deal specified that Bill do something for Gideon first. Then Gideon would have had an obligation to pay Cipher back–an obligation that he clearly could have disobeyed at any time. Gideon called off their deal when Bill failed with 0 magical repercussion.

Similarly, Ford made a deal with Bill that let him possess him indefinitely. Ford grew disillusioned with Bill and took steps to physically prevent their deal from being fulfilled (his metal plate, that is). This didn’t break any kind of supernatural contract because no such contract was ever being enforced in the first place.

Bill’s a con man. He makes you think you have to give him something when you don’t. He makes you think he has to give you something when he won’t.