Getting decent staff to work in retail is a real headache, ask any manager of a chain establishment. Doesn't matter if they serve coffee, bikes, DIY supplies, beer or catalogue goods, they all have much the same problem recruiting then retaining reliable staff with a good attitude.. The money isn't great (and managers often have no discretion to pay good staff more), the hours can be unsocial, plus the prospect of having to serve rude members of the public with no manners, doesn't make it any more appealing either. How many people reading this with a decently paid job on fixed daytime hours Monday-Friday, would swap for one in retail that only paid half as much, and involved all sorts of early starts or late finishes, weekend shifts, bank holidays, flat rate overtime pay etc?
I'm not excusing bad service and an indifferent attitude, but ultimately the jobs that offer the best money and conditions tend to get the best staff. The min wage outfits can generally only attract the part-timers, between-jobbers, students, drifters, and semi-retirees just looking for a bit of beer money but don't really need to work. The calibre of such staff is very variable and good ones tend to jump ship as soon as something better turns up nearby, so you get high turnover too.
It boils down to how much of the price of the product you are buying are you willing to see go into staff wages rather than the actual cost of the product itself, and the cheaper the goods the greater the shop wage overhead as a percentage of the transaction. It's the only overhead the retailer has much control over; things like rent, rates, and utility bills are pretty much fixed. Paying flat rate for working weekends and no sick pay etc might shave a few percent off their costs but it also makes working for that employer less attractive, so they get lower calibre staff. Years ago, you'd often see a "Saturday boy", a teenage schoolkid, doing shop work just on Saturdays for extra pocket money, which was a useful source of labour and meant less compulsory weekend shifts for the regular staff. That seems to have died a death.