Hum... the "limit" is so subjective and it goes up as I set my eyes on higher price bags... I went from LV now to looking at Hermes... over $100 just isn't going to get me anything.
I do think it depending on what I am buying.
If I purchase prelove bags I will not pay over 1/3 for something that is obviously used and discontinued. For a currently sold at boutique bag, I will not pay over 1/2, if it seems used. I probably pay 75% for something new to like new. However, if it is a LE piece and I really want it, I might be willing to pay more.