Aside from keys/crates/cards, most of the items sold are genuines (which you usually get as rewards for pre-ordering other games) and unusuals (which have to be unlocked from crates, which require a key, which costs real money). You can sell some strange weapons and tools as well, which are dropped, but they tend to sell for very little.
About 1% of crates contain an unusual, the rarer of which are worth lots of money. You could buy lots of keys and lots of crates and hope to make a profit in the long run, but the fact that there are others doing this, combined with the laws of economics, means that your expected net income would be very small.
(In fact, there is a whole TF2 black market where keys bought/sold using stolen credit cards. Because of this, your expected net income will actually be negative)
So yes, you can make a very small amount from some of the random items which are dropped. But no, you shouldn't expect to sell any of them for anywhere near $10. Those are typically the ones unlocked from crates (which cost keys = money), and you can't expect to make an overall profit from them (unless you get very lucky in your first few crate unlocks).