The game you get is random, you can't choose. However every game has a normal value (for example $10 on Steam).
1 random Steam game = $0.4
So how can I know what I pay for?
That random..... So you can't know.
Like lottery
Thats not random. Thats blind pay and get a cat in a bag.
Random is when there is a list and you get some of games from list.
So I think that seller is selling bad games which nobody wants. Thats why he is selling like unknown games and thats why they are cheap.