I kinda understand what you mean especially when people sell clothes or reorderables, some people do ask way too much. Usually they factor in "labor costs"... I usually just sell them for store price, but some stuff like the grace seasonal stuff I'll up it a little more if they aren't available at the moment or just make people go to my store and just buy it directly.
Lots of stuff are rare or unorderable and that's why they're more expensive, I understand that. Usually items like the regional DLCs or items that aren't readily available like the holiday stuff are harder to get instantly and that's kinda why they're usually in the millions.
However, there are major inflations that have been happening since the game started vs now. I remember buying gold roses for just 20k when I started last year around this time or at least trading 1:1 for black: gold roses, and now some people are selling/offering like 100-500k each and doing 2:1 or 3:1 for hybrids:gold roses. Yowza lol!
It also kinda sucks though since bell tree has the TBT system people are able to get ig bells much easier which somewhat breaks the game, but idk. What can you do? People offer how they see fit.