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 = $0.4
So how can I know what I pay for?
That random..... So you can't know.
Like lottery
Thats not random. Thats blind pay and get a cat in a bag.
Random is when there is a list and you get some of games from list.
So I think that seller is selling bad games which nobody wants. Thats why he is selling like unknown games and thats why they are cheap.
If you wanna join steamgifts.com, this is best way to join because website need 100$ games value.
If these not form bundle you can join steamgifts with cheapest way.