Gun question: Chamber erosion in revolvers

Okay, my local Army-Navy has a decent little used five-shot .38 Special Rossi revolver for $149. I’ve checked it out. There’s not a lot of play in the cylinder, the finish is decent, it definitely seems like it could be worth the money.
However, there is a certain amount of corrosion in the cylinder chambers. I know this occurs in in all revolvers in the chambers just ahead of the case mouth; what I don’t know is how much of this is normal. Is it something to worry about, or am I going to find it on any revolver that’s been fired more than a few times?
It’s not a lot of corrosion, it just looks like the chambers need to be swabbed. However, the store employee told me the gun had been cleaned, and the barrel did appear to be clear.

Well, it’s irrelevent now anyway, as I went and bought it last night!