I could easily fill in holes in my collection by buying cheaper online. And I often do. But I also have a major problem where I get to a con and start digging through long boxes and the lizard part of my brain is like "GET IT NOW" and I just end up over paying. I don't really care that much usually but I paid quite a bit for a pretty pristine copy of Uncanny X-Men #134 (first appearance of Dark Phoenix) that I probably otherwise wouldn't have.