does that bother you or not? Personally, i try to remove any stickers price or otherwise (unless its the original price tag on a box for instance). A thrift store price tag I think is kind of tacky to leave on. I'm sure most people know the odds of stuff being thrift bought, i personally dont feel the need to rub the idea of "I paid $.99 = you're paying $20" in anyone's face.
Just my 2 cents.
~bill