If they are my favorite authors and books, then under normal circumstances, I would never sell them for cash. This is a very precious collection for me, not to mention the author's signature. However, there are exceptions to everything. When I really need money badly, I may consider selling them for cash, but I think the possibility is very low. After all, no matter how good the paper book is, the price will not be too high, even if it is signed by the author, because the book can be produced continuously, as long as the author.
If it's a book I don't like very much, after all, radish and cabbage have their own tastes, and my favorite book must be tasteless to some people. On the contrary, books I don't like must be read by some people. I don't like such books, and I won't get much attention in my hands, so I will consider selling them, but not for how much money I can sell. As mentioned above, books are generally worthless, but in order to find one for this book.
But generally speaking, I won't choose to sell paper books signed by the author at high prices online. What is really valuable is the content, not the book itself. Books are for reading, not for price hikes.