It's interesting that I get so many twitter followers who are authors. Most of them never say anything to me (as is the case with most followers), however I occasionally get one noticing that I am selling their title. They usually just point it out, or ask how many there are, and I respond, and that's the last I hear from them. Since I don't know why they're asking, I can only guess that it's a surprise for an author to see their book at a bargain price and they're expressing that surprise by saying they see it.
I know from previous experience that this can be an unpleasant moment for an author, so here are a few points to consider:
1. Most of what you see on the bargain market are not remainders, they are "hurts," our word for returns which have been sold in huge lots to wholesalers who sort them out and sell by title.
2. For your books to show up in returns, they had to have sold in some significant quantity. If you see big numbers, they were probably used in displays, which means they were used to sell even more of your book.
3. Even actual remainders, which might have a bigger negative connotation for you, aren't entirely a bad thing. Yes, your book is no longer on your publisher's list, and you no longer receive royalties, but there are now potentially thousands of new readers for you, people who would not otherwise have picked up your book.
Lots of my customers are outside the traditional bookselling channels, as I am sure are lots of customers of my competition, so you are now reaching new markets, all over the world.
Those new readers might be waiting for your next title and they might not wait for it to show up in bargain or used next time.