On the rare occasions I'm going to be in a different locality where there's an unknown folk club night in the vicinity, I always try and contact the club in advance to see whether it's ok to do a floor spot. This may save the club organisers embarassment in having to say "no" to the floor spot to my face, and may save me the need to lug my guitar to the club.

I give the club links to my website and YouTube channel, so they can see what they might be letting themselves in for...

Of course, the club may advertise itself as a "come-all-ye" - in which case, I might risk it.