Ok,

I was able to contact a concierge concerning an upcoming stay and he was able to both provide me with tourist information, but also has made (at my expense) arrangements for a limo and greeter to meet me at the airport.

I want to thank this particular fellow and his assistant concierge, but I don't know the proper policy for doing such. Would a twenty dollar bill in a plain envelope be acceptable? I know that people with that position are supposed to answer questions, but I think it was really nice of him to help me with a car service.

What's the best way, not violating a social norm or breaking rules to compensate a staff member? Cash? Box of candy? Sending an email to the GM? Half bottle of Glenfiddich?

Chuck

Most luxury hotels have either their own car service or an arrangement with a car service company. This is highly profitable for the hotel. It's not really a special request, like getting a prime reservation at short notice for a restaurant that's otherwise fully booked well in advance.

He upsold you on a perfectly normal hotel service, doing his job. If a concierge isn't supposed to be answering questions and doing precisely what you described then what exactly is their job?

The concierge did his job, great. You should say 'thank you' and that is about the end of it.

Your best thanks was the comission he/she gets for arranging an undoubtably overpriced hotel meet and greet service.

It does not seem like he did anything above and beyond.

Cash tip.

The tourist information was simply a basic part of his job description. The arranged limo ride will compensate him for booking it.

If this guy got you into Per Se on two days notice, at 8 o'clock on a Saturday night, then yes you'd probably owe him a nice tip. As it stands, he just did his normal function.

No tip. It's their job and either they or the hotel will be on a kickback for arranging the car booking.