Be Willing to Change What You Sell
When I first joined eBay in 2002, I was only selling my college textbooks to the next poor starving student. A couple of years ago, it occurred to me I could underwrite some of my thrifted purchases by selling some items. In lockdown, I listed everything that didn't move. It was then where I got a sense of what would sell and what wouldn't. Be willing to make changes in the product you are selling.
There is also a feature as a seller where you can block buyers. A couple of months ago, I had one buyer message me complaining about the price of a sewing pattern. Rather than make a reasonable offer, buyer prattled on about the price. Said buyer was blocked from future bidding or contact.
On the subject of sewing patterns, I call them my little "money packets." I had collected patterns for years, just because I liked them. I also scanned in the front of the pattern packets so I could post a Pattern of the Day.