Shipping a 1/4" x 1/4" piece of rubber in a plane white envelope doesn't ship for $0.55, it is now an irregular shaped parcel and can not run through the USPS mail system and when the envelope gets torn open (and it will) and the part is lost you have a dissatisfied customer and your reputation gets harmed.
I have bought parts from members here who did not properly protect the parts. The parts got damaged, in one case it was NOS and one was Unobtanium. I do not do business with those sellers any longer, PERIOD!