Hmm, the last times I've played in a music shop...
Once I took in my own bass because I wanted to try out some practice amps (and bought one).
Once I wanted to try a used bass, and bought it (ok I'd decided to buy before I tried it...)
Once I was invited to try a very expensive one for the fun of it and ended up leaving with a Squier...
Twice (two different shops) I bought a pedal and was invited to try various things.
Once I asked to try a guitar stating I was just curious about it. Then they told me the price and I accidentally bought it.
Once I went in for a lead and they persuaded me to try an EUB, but I gave up after about two minutes.
Once I bought a mandolin case and got invited to try a Hofner.
Went in with my brother and his wife, he was buying her a guitar and we all got involved in various tryings out.
Buying a tiny blackstar amp, just wanting something to see what it could do.
Went in to kill some time, got into a conversation about lovely Masterbilt epihones and got invited to try despite saying way outside my budget.
Thinking about it, a common thread is engaging with the staff rather than just saying 'can I try x'.
A second one is I shouldn't try out things I'm not expecting to buy.,..