He didn't. In novel there isn't the scene that old fart suck his nipple. It just mentioned he was flirting with them and sexually harassed in the alley which karel mistaken he was doing it for sponsorship. Sasya was portrayed as selfish guy until the end. Sasya pov on last chapter was truly heartbreaking. He actually wasn't bad at all. It just how this story goes. Even media keep slander him.
Ah so the thing that happened was
Sasha had heard of Skar who had a physical profile same as Karel. So he wanted to meet him so bad, he attended the parties. In order for him to attend these high profile parties, he pretended to be someone who needed sponsors. The fat guy wanted to him but consented only for chest licking. As he confirmed who was skar, he was so desperate to meet him, hence the fellatio incident. As you have read, he was very hesitant but thankfully Karel arrived on time.
So, it’s a gray area for this question if you consider consent for chest caresses and licking sex.
Otherwise, as other spoiler alerts, he never did sell himself. He rose up by skills alone. He never had any physical contact with anyone except for scenes mentioned
If you all talking about novel, then it really sucks. It’s so much better in novel and makes SO much difference for their relationship and Sasay character. I don’t eve care that much, but I even feel sad about this dumb changes from novel. Cause it feels like all events leading up to meeting Karel have barely anything in common. Especially scene with old fart.
People who read chapter 20 and still think Sasya didn’t sell himself/sleep with others, what did you think happened where? Old dude just kept sucking on his nipples all night long? Please tell me you aren’t that dumb?