It can if they have time to get up to speed but if they're thrown right at clients/customers probably not. I consult and develop on a very complex platform, both in breadth and depth. I routinely have to correct their sales/marketing people and account executives on platform capabilities and even pricing/licensing. I try not to do it in front of clients but sometimes have to. You're right in that it doesn't go well.

edit: actually, i've seen this work. The marketing person has to be honest and upfront about being new and take down any questions they can't answer and then follow-up. I've found clients/customers to be sympathetic, everyone has been thrown into the deep end at some point in their career. A humble and honest approach can even endear them to the customer. So, it can work but the you have to upfront, honest, and absolutely follow-up.