What's the difference between the iPhone 3gs refurbished and the iPhone 3gs refurbished cosmetic blemish?

What's the difference between the iPhone 3gs refurbished and the iPhone 3gs refurbished cosmetic blemish?

No

The one with the "cosmetic blemish"
has an imperfection that you can see on it.

In the absence of any other information, that's the whole story.

The scratches may be more obvious on the one tagged cosmetic. It'll still work the same, and both will have scratches if you look hard enough.

Don't expect much, or pay much, for this model. It's on Apple's "Vintage" list in the US and on the "Obsolete" list everywhere else, and there won't be any iOS updates.