I had a similar difficulty with an
ebay seller a couple of years ago, but the lag times were in weeks, not days. Two weeks and no stamp. Sent e-mail and no response. Four weeks and no stamp. Sent e-mail and no response. Filed negative feedback on
ebay and got a really nasty e-mail vilification from seller. I was tempted, but did not respond to it. Received stamp a week later. I added seller to my own black list of sellers (two total) and will not do business with them.
Donald