Its simply not practical from a time/cost standpoint to list something like a mint 2149a single on
ebay (time to scan, describe, upload to
ebay, record sale, ship, not to mention the eBay/paypal fees).
I recently tried listing some mint modern US multi design blocks of 4 and got no takers. Did everyone already have them? Did I not list enough of them for someone to bother with an order? Were they priced too high (priced to net me a hair over face after allt the fees)? I don't know, but I'm not planning on wasting my time repeating this again anytime soon.