Yeah natman, I do that. That's why I stop. But I always wonder afterword if I wouldn't really have paid just $5 more.
If you have any second thoughts, your maximum isn't really the maximum. The key is to make it more than you really want to pay and as high as you'd ever possibly go.
You have to make yourself sincerely believe that even a dollar more is way too much and to feel relieved if it goes over.
The key is sincerity. Once you can fake that you've got it made.