Ahhh tipping. The most offensive part of the tipping discussion is the part where people believe that their way is the absolute right way and all others are wrong. Don't tip. Do tip. Tip a lot. Tip a little. Make up for low wages. Force them to live on low wages.

Here's my take on tipping: I do whatever feels right at the time.

I've tipped appliance delivery crews $20 each for a TV that they unboxed and left on the floor because they did so very gently. I've tipped $0 to the same guys when they scratched my floor ever so little when delivering and installing a refrigerator. Regardless, they always get offered a soda or bottled water or something like that.

I tipped some movers around $60 each for a half day of work moving about 8 pieces of furniture because they did a good job of putting down pads and not denting anything. I was going to tip $20 each, but they did a better than expected job on a very hot day.

At a restaurant in Italy, I may not tip at all if the service is only passable, or I may tip 10% if it is great or if we put them through a lot of hoops.

In London, a pint likely won't get a tip or a 'one for you' unless there is some friendly banter.

In Italy, I've tipped between 0 and 20 euro on a 60 euro hired car fare all dependent on how friendly, helpful, prompt and efficient the car service is.

Here in the states, I tend to go with 15% unless the service sucks. I'll go as high as 20% if it is a place I frequent and they know me, and treat me as such. I have adjusted the tip downward when the tab includes wine or expensive cocktails.

Aside from meals in the US, I tend to view the cost of the service to be the price, and any tip to be reflective of doing a better than expected job for me.

So tip however you'd like.

To the OP, I'd say the $20 is appropriate. It's a long drive and they may not be able to get return fare...sounds reasonable.