selective customer service from cashier

While most of my shopping happens at Spar Meyersdal I do enjoy relatively good service from that branch, however yesterday my interaction was poor to say the least, some cashiers just give poor service and I sometimes just let it go, however yesterday’s cashier does not greet when greeted and mumbled something under her breath that does not remotely sound like a greeting and then asked if wanted a plastic bag, and then placed the bag on my items after it was scanned and then took the money, great I thought and a bit annoyed as it is usually packed, I took my change I packed it myself, and just then another customers is being served, with good interaction and even packed this customers goods Normally i would just move on and let it go, but this lead me to believe that this cashier is plane down selecting who she delivers service to or is just being ******, either way whatever the reason, it is really a poor reflection on this branch, it may sound simple and meaningless but how many others is this cashier selectively treating differently from others , this is really poor, Spar Meyersdal treat your customers fairly