In the fanfic community, the verb to beta means to edit (and/or critique) someone else's story. Ceciliaregent points to some entertainingly bad offers to beta from people who really aren't doing a very good job of demonstrating their skill with grammar (or rather "grammer"), spelling, and punctuation.
Sure, nobody writes perfectly all the time; and there's always Hartman's Law of Prescriptivist Retaliation to contend with. And yeah, even some English professors aren't very good at spelling. But if you're going to offer to proofread someone else's story, it's probably a good idea to spellcheck your offer. Or else to, you know, be good at spelling.