I think a large amount of people here "flip" some books to fund collecting, and I see nothing at all wrong with that. And I imagine there are also a lot of people that just happen upon deals too. In the last few years I've found two New Mutants 98's for under $5. I didn't steal them, mislead someone trying to sell something they were unfamiliar with, or even haggle on the price. Should I have passed those up when I knew it meant finishing my New Mutants run and selling the other to purchase other books I needed?
And I'm willing to bet no one here has forced anyone to buy a book for a price they weren't willing to pay.