Commentary for Kiddushin 125:8

According to Resh Lakish, the man must also give her kiddushin money. The fact that he will perform a favor for her is not sufficient.

The two baraitot cited here prove that a man can betroth a woman by performing work or some sort of favor for her as long as that work has not yet been done and it is worth the value of a perutah. So this is a refutation of Resh Lakish.