Fic Reading Question

If you're reading a fic that seems littered with spelling and grammar errors, would you give up reading or would you offer proofing assistance?

I'm reading a fic over on FFN and the plot is interesting so I'm continuing. The author's bio says nothing about English as a second language so I made no mention of that in the PM I sent her offering my help. Do you think this was a step too far? Her author's notes seem to welcome constructive criticism.

I was just wondering where the rest of you stood in this matter.