For me, samsung pay works really well but can be finicky. I have found that if you go to long without clearing the cache it will beep, go through, then say transaction cancelled, tried this both with nfc and swipe. As soon as I cleared the app cache it worked fine. And yes, this was through multiple different stores. It also can be finicky when trying to locate the reader, most places work fine but stores like total wine have it in a different spot, at the very bottom instead of the middle and you have to put the phone there, that is why I wish the reader had more power.
Some stores like walmart, home depot and lowes it will not work, most of the time, if you are trying to use a credit card. If it is a debit not a problem. Only one place has it never not worked at all, Ziggies home improvement, beeped, nothing, not on nfc or mst.
Someone needs to step in and make standards for mobile payment.