Cassette tapes can be sold on eBay by creating a detailed and accurate listing, complete with pictures and the condition of the item. Check pre-existing listings at eBay on cassette tapes in similar condition to determine a price for each cassette tape.
The cassette tape is of saleable quality if it is playable by a device. It can be used or new, and it can be blank or have a soundtrack already recorded. Multiple cassette tapes can also be sold in the same listing. Cassette tapes are eligible for media mail, resulting in a cheaper price to ship to the buyer.