Lately I've been getting a lot more FQs and fat eighths without selvage...they're folded in so you can't tell it's been cut away unless you completely open them up & some are labeled shut or tied so you can't see before purchase.
In fact, I just bought a fat eighth from JoAnns Wednesday and it has no selvage whatsoever. The tip about slight stretch is a good one and while the 18 x 22 is usually true from fabric stores, if you purchase online or trade with people, it is not always the case.