It's not just about having player shops (imo that's not even the issue with rare items hunting on PSO2), there's just way too many random elements to rare item hunting on PSO2, and the way quests are (not) designed in PSO2 makes it just not fun to hunt for items.
First about there being too many random elements, not only the drop rates are usually way too low for it to even be fun to hunt for these, there's quite a few rare items that aren't even huntable, they're locked away on quests that can only be played through small periods of time at random times (unless scheduled), the emergency quests.
Outside of EQs, the better rare items are obtainable on multi-party quests, quests where groups of 12 players run in circles mindlessly defeating enemies, with 12 players there's no skill involved in running these, imo there's too much chaos going on at once to see what is even happening, too many shiny effects from 12 players attacking the enemies and such. These quests don't feel like dungeons either, with the way they're designed for large groups of players to run in circles defeating enemies, they feel more like "farms", as in, designed solely for players to farm for rare items, there's no sense of progression through these quests.
Quests wise, I feel that what PSO2 is lacking the most is quests that are more like PSO1 and PSU, that is...
- single party quests, quests that can be done with a max of 4 players, but can also be done with smaller groups, like 3, 2, or even solo, one of the biggest problem of 12 player quests is that these games are more fun when playing with friends, but in 12 player quests a player has to rely in random people (it's much easier to get a group of 3 friends to play than 11, after all)...
- quests that are pick and play friendly, being able to join anytime during the run, the advance quests on PSO2 with their capsules restrictions make them the complete opposite of this...
- quests that can't just be rushed to the end or where their goal is not simply running in circles until a set number of points is acquired...
- quests that use set maps instead of being completely randomly generated, areas that actually feel like a location, and sections that need some sort of co-operation would be nice too (switches that need 4 players to reach a certain optional location and such)... the way PSO1 did the free areas was the best one imo, a few variations for each area and randomly choosing one for each run...
- quests that are somewhat long, I'd say at least 40+ minutes long, most quests in just PSO2 feel too short...
- and of course each of the quests would need items worth hunting in them.
TAs den is probably the closest to what I'd want to have more of in PSO2, except that it's locked to randomly/rarely appearing for those who run time attack quests...