That's pretty harsh. I understand that it's silly to not proofread very carefully when doing a stunt like this, but language mistakes aren't a sign of incompetence.
Language mistakes are not, but not having your document proofread before you illegally litter it all over a parking lot is.
Grammar mistakes are a sign of laziness, not incompetence. Both should be warning signs.
Right, by incompetence I was referring to the parent's comment towards the guy not being able to build a quality product because he left an apostrophe out of a word.