Blocking sellers? No.
But...
If you don't promote, your items will show up on the search results page and that's about it. Promoted Listings (PLS) show up on far more pages, such as listing pages. So, right there, you are at a disadvantage.
If your competitors do use PLS effectively, they gain the advantage of better placement on the search results page AND all the additional placements on other pages.
So, it may seem like ebay is blocking your sales, but what is really happening is, your competition is blocking your sales by advertising.
Of course, depending on what you sell, what sort of sales velocity you want, etc, you can do without PLS. But it's like any business where advertising matters: if the other guy is advertising effectively and you aren't, you are probably going to find yourself struggling.
I no longer think of my ebay store /listings as an "ad".
I think of it as a store. It is there, in this huge business district, and I hopefully get some traffic. But if everyone else in the business district is advertising, and I'm not, I might have a problem. So, having an ebay store is just a business. A business I need to advertise and promote. And so I do.
