You don't have to tip anybody at airport except the luggage guy - the one at the drop-off/pick-up zone who gets the cart for you, loads the luggage and pushes the cart for you. feel free to tip him whatever the amount you like - typically $2-5. You may wish to not tip him - he does not expected you to tip him but IMO - that's rude 
hotel - same thing with bellhop. and valets. you should always leave a tip for hotel cleaning maid after you check out - $2-5 is fine. You don't have to pull the bed sheets. They will replace it anyway. Most hotels have a policy in order to save water - if you leave the towels on floor - they will clean it. If you don't, they assume it's clean. Some people are germophobic so it is not uncommon for customers to request for a complete towels change (and even bed sheets) when they check in.
