I will get a swarm that is only a few miles away for free. (some people want you to pay them...)
If it's much of a drive at all I skip it. And you have to learn to ask the right questions:
1) how high is it (take their answer and double it)
2) how large is the swarm (take their answer and half it)
3) did you spray it (it doesn't matter that they said "no", the question is, did they hesitate when they said "no")
4) how long has it been there.
5) describe it (you often find out they are NOT talking about a swarm at all, but a colony of something living in something, often a nest of yellow jackets...)
6) if it's not a cluster on something (swarm) but "bees" flying in and out of something, get a description. Ask it's shiny and yellow and black. :)