This thread might be of interest:
Used cycling shorts?
Note post #26 in particular for a reason not to buy used bike shorts.
And my own small contribution to the thread:
This reminds me of a conversation I had with an employee at my local bike shop. I had to get a pair of shorts replaced under warranty - one of the seams opened. He held the bibs at arm length by a shoulder strap.
"Oh come on Pete, I washed them before bringing them in here" I said.
"I'd do this even with my own washed bibs, and I KNOW where those have been."