Ive used the Local Nissan Dealers L2 a hand full of times. They don't have a CHAdeMO. I have no problems with using that one, as they already got a Crapload of business from me before I bought the Tesla. They would have Gotten my Leaf Business too if Nissan had a Leaf that got the range of a Model S. On top of that, I have no problems going in and getting a free coffee and a doughnut either. But, once again, I've already spent plenty of money with that dealership, and, I also feel, looking back on some service I had done on my truck before getting the Model S, that they really Hosed me. Hindsight...
As for using a other dealers station, I will usually, unless signage is posted, just plug right in as long as I'm not blocking anything. After plugging in, I will go inside, and speak with the manager. I usually say Thank You for providing this much needed service, and can I pay for my electric usage.
It's more along the lines of "easier to ask for Forgiveness, then to ask for permission".
Just for offering, I've never been asked to charge. In fact, usually, at that point, I'm invited in to relax in the customer service lounge, and use any of the customer amenities available.
I would like to point out a VERY kind BMW dealer in Erie, PA. When doing my niagara falls trip in 2014, I found myself, despite driving extra slow, and leaving the supercharger with a range charge, grossly short on range getting to Niagara. We stopped at the BMW dealer (Forgot exact name off the top of my head). On route TO Niagara, they actually thanked me, as they just had the Chargepoint installed the week before for upcoming I3's, and had no way to test the station. Invited us in etc...
On the way home, they even offered to have the dealership shuttle drop us off (And pick us up) at a restaurant. We accepted. I offered to pay, they said no, just tip the driver. So that we did.