Most people don't know that a swarm has a value to a beekeeper. Once word gets out to the public at large they'll be phoning round seeing who makes the best offer.
As things stand, they're just too happy to have someone take away what they see as a threat to their safety. Many years ago a swarm landed in my office car park. I found the local society's helpline, called it and someone was there instantly. I was grateful. Now I know better, and think it's more than a bit opportunistic to ask someone to pay for your petrol for driving over to pick up what is, in effect, a bundle of twenty pound notes. That said, if the swarm is in an awkward position, and requires the use of tools and a lot of work, perhaps a seeking a contribution is justifiable.