My wife buys and sells a lot of stuff on eBay (500+ transactions), and one thing she has learned is to be patient - up to a point. Example: last week an item was overdue, and the seller sent the tracking number to her. When the number was entered into the USPS tracking site it said no such number. The wife was incensed and wrote a nasty e-mail to the seller. Yesterday the item showed up ten days after it was mailed - it had a tracking number but it was one digit different than the one the seller provided (typo). It should not have taken 10 days to arrive, but it did through no fault of the seller.
OTOH there are sellers who do cheat on-line buyers, we've been swindled too. Sometimes there are extenuating circumstances in the seller's life which take precedence over mailing an item - health, deaths, hurricanes, etc. Those can be real excuses, or they can be lies to put off the buyer. Just food for thought.