I think it all depends on what your avenue to resell stuff is. I know some people try to buy stuff on ebay and resell it on ebay. Yeah you can occasionally get good deals or a steal, however since ebay, especially auctions, kind of determines market price basically whatever you buy it for is going to be around the same as whatever you can sell it for unless someone maybe does a 1 day auction, starts it really low with no reserve and you really get a steal. Even if you get a good deal your looking at 10%-13% in ebay and Paypal fees so not a ton of room to make money.
As some others on here have said though, if you have avenues to move stuff off ebay or even better out of the country where you can bigger premiums it could be a way to make some money. Sounds like a lot of work though. I occasionally see people buying from me attempting to resell on ebay but most lose money