First and foremost, I assume you were going to do this for free. When you do this, you take money from the pockets of those that charge for this service. Additionally, you become known as the guy that will play for free, thereby eliminating your paying gigs. Finally, that amp will likely be stolen by the next day after you leave it. Other than that, go for it!

Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)