I've noticed that a lot of music artists and music groups sell products before/during/after a performance. While they could easily use Square or a similar product, some of the tablet or mobile solutions also work quite well. If your product sales exceed $60,000 annually then you may want to take a look at Bindo POS or NCR Silver since these programs have payment plans available that can be turned off and on as your performance schedule dictates.
Plus, you would have the option to pick and choose whose handles your credit and debit card processing (commonly called "merchant services"). The mobile solutions also very portable making for easy setup and teardown.
At the very least, make sure that you are equipped to accept debit and credit cards as payment for your merchandise as your fans tend to spend more when not using cash as payment.
More reviews on Bindo POS can be found here: https://bindopos.com/reviews
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PS - no promises but I might be able to connect you with a company that will provide you with a free point of sale system in exchange for free advertising. I'm sure that your fan base includes people who own or manage retail stores and food service related businesses. The sort of arrangement also makes for a unique press release that would provide additional exposure to your music.
Are you in the US and in need of no cost retail point of sale advice? I'm happy to help and can be reached on my cell at 208-340-5632 (I am on Mountain Time) or via email at email@example.com. There is also a contact form to the right that can be used to reach me.