how can somone stuff up so much...

Take all the evidence, photos if need be, Hope you took photos of the missing bolts, other it your word against his) and drop it on his front counter, (be half respectful and don't do it in front of other customers.)

If you approach it right I doubt he'll ask for any money at all. Go in there acting like d**k (eg: dont go in there with same sarcasm and smart a*** comments that you've been using here.) and you'll only make a bad situation worse.
Just remember, Yes there are bad mechanics out there, but they are out numbered 10 fold by bad customers.

Rule number one should be if you suspect a mechanics gonna stuff up you're car let them then call fair trading when it's stuffed, not go in and do it yourself.
Either way I wouldn't even go back in there haha