This discussion just seems to be a preference between the extremes of "the customer is treated as always right (reminds me of me Sears retail days) vs the seller can do whatever they want as they are not obligated to serve anyone (Seinfeld soup nazi).
One one hand, the customer should be treated with dignity regardless if their perceived economic ability appears to be inadequate.
On the other hand, the seller is trading his time, energy, resources for income aka money. It’s not unreasonable for the seller to try to maximize his efforts to maximize their income which is especially motivated if they have a family to support. This can entail weighing the probability of their spending time and effort vs making a sale, this seems reasonable. Perceived avoidance of wasting time/effort, especially in a work environment, is quite common.
So, on the scale of things, the seller has freedom to be self serving vs the buyer not satisfied with the seller’s lack of proper customer service I’d have to side with the seller as having more weight. To choose otherwise would seem to enslave the seller to the buyer’s expectations at the seller’s expense.