Interesting, the responses are totally opposite of what I'd expect.
When I was selling regularly on Ebay December and January were miserable. Hardly any sales at all.
As a buyer, I'm far more active during summer for a couple reasons.
First is that we live in a good sized Victorian house. Which costs a lot to heat
So I'm largely broke from Nov-March/April.
Second is that my work is seasonal to the summer, so In addition to not having the huge oil bill I also have some income then.
Steve B