After 25 years in the discus hobby, I only purchase from Simply Discus sellers, and one other seller who used to be a Simply Discus seller. Here's why.
QUALITY - There are many fish stores in the area which carry discus. I've never seen one I want in my fish room. The fish store owners know that they have plenty of customers who can't tell a high quality fish from a poor quality one. SD sellers have to deal with a much more advanced clientele. Even the new hobbyists will post their discus pictures. If the quality isn't there, someone will comment. If there's a disease problem, someone will comment. So you can guarantee quality.
PRICE - Fish stores do a 200% mark up on all fish, so a guppy that wholesales for $1 is priced at $3 in the store. SD sellers have much lower markups because they don't have to support a brick-and-mortar enterprise, meet a monthly payroll and cover loan payments used to start the store. Their prices may be just as high, but that's because their starting stock is much higher in quality. In contrast, the disease section of this forum is filled with discus from non-SD sources.
Don't ever buy fish from an online aquarium store. Use them for dry goods when one box is the same as the next.
Willie