Except if you're the one using the words 'writing skill', you're communicating "I'm looking for people better than you." Which is a pretty shitty thing to say. Specify what you're looking for. If it's grammar tell them their grammar is not up to scratch for your liking, if their sentences are confusing point that out. Never use the term 'writing skill' because it's such a broad term that doesn't relay any message other than one of "I'm better than you". Even if you don't want someone to be part of your RP, you should treat them as an equal.

Other than that, ain't got nothing that hasn't been said.