When I am playing poorly I would rather have someone tell me than to play with me and mentally note not to ever play with me again.
For example, the other day a group wanted a healer for deleera's. I haven'y played my cleric since before the EU transfer and I never played one past level 7 anyway so when it comes to clericing I am pretty poor. I told the group that though up front so when one of the team said 'Umm...can you heal so-and-so?' I apologized, mentioned how I was trying to catch up (the group was running pretty fast for me) and will try to be more alert.
I just wasn't used to healing people so quickly. But, I will get better at it.
So, yes I expect it if I know I am not a great player, but I always tell people ahead of time. Especially with LFMs that say 'Know the Quest'. I send a tell first explaining how I may not be the most knowledgable of it, if they accept me, then I expect 'some' critiscm but not a flame.