What did you learn from reading the fine print?

Mentioned this story on Tildes before, but I was helping a friend of mine purchase a car and ended up catching something in the contract's fine print that saved like $4,000 at the end of the day. He went in knowing the exact car he wanted, just wanted to find a good deal since he wanted to lease first then purchase the car. Talked to a salesman and everything was going fine. The salesman had told us a price, my friend agreed to it, then an hour later when it came time to sign documents, the monthly payments on the lease were fine, but I noticed that the buyout price at the end of the lease seemed a bit high. So I did some quick math and realized the total price paid for the car (lease payments plus buyout) would actually be higher than what was previously discussed. Brought it up to the salesman who said I must be mistaken. Then we got the manager involved who said there's no way they would have offered that price because it was too low. So we say then fine, we'll leave then since this isn't the price we would like. And then suddenly that price was fine and they were totally okay with it and 'oh gosh you drive a hard bargain we are gonna LOSE money on this deal hahaha....". Scummy as hell and I'm sure a lot of people fall for it.