Unlike other krogan on Tuchanka, Ratch shows a certain tolerance for "aliens" like Shepard. When asked about it, his charity turns out to be out of need rather than nobility: he asserts to have spent enough time off-world to know that aliens tend to carry more credits than locals, grumbling that he can't afford the luxury of turning away paying customers.
Nevertheless, he requests Shepard's help to eliminate vermin which are getting into the krogan's food stocks. If Shepard helps him out, he offers discounted items at his shop.
If Shepard buys pyjak meat and feeds it to the pet varren named Urz, it starts following Shepard around. Ratch amusedly comments on Urz's liking for Shepard.