When you bring a big event to a venue you are creating an immense amount of work. You're only there for a short time, you show up for a few days and then leave. They're there all the time. A janitor can make or break your conference. Can you imagine what 1500 people do to a venues' washrooms?
Before our events, we always go and introduce ourselves to the staff. We try to keep things friendly and it's always paid off for us. I hand out my business cards to every staff member from hotel clerks to cleaners to security guards. If they have any problems or questions, they have my personal cell number to call.
If we have pizza brought in for the volunteers, we always offer some to the shift workers there. We try to be pleasant and courteous to the staff ahead of time, you won't believe what a huge difference it makes.
On the 2nd day of our last event, one of the security guards bought me a screwdriver set out of his own money because he saw we needed one. Doesn't always happen but people can surprise you.