i've never understood how to do it. i mean, i've asked them for restaurant recommendations and to secure tickets for stuff for me... but do you pay them?? do you tip them?? how (i.e. just walk up and hand them a $20? ask that it be added to your bill??) or is it just a servie the hotel provides?

for example, i'm staying at the hyatt berlin and called ahead to have the concierge secure some symphony tickets for us.