If the first thing the store does is list stock the second thing it does is thin out the stock that does not sell. i is not quite that simple but it is the next goal once the store is up and running.
Expansion is common in business. Once you are successful become more successful. I've never understood the real world business idea that a business is only successful if it grows each year and it is not successful if it does not grow to some benchmark. Eve is going to limit how much your store can grow. The populace is not stuck in one spot. 7-2 has a home system yet moves for days or weeks at a time. Right now all of Eve it seems is grinding Sisters of Eve loyalty points meaning normal mission hubs are abandoned echo chambers.
With 7-2 gone my attention is split across two stores in different regions. It is a major pain in the ass. I have no other way to describe it. I spend time patching holes in both sides but I can't stop all of the leaks. At the moment for instance I am fighting a war in Solitude for Cynosural Field Is. Someone keeps buying them and relisting them at just under three million. I ran out of stock and had to skip a day. How dare real life intrude!
When I started the market I tried to stock some over everything and everything tended to sell in fits and spurts that made little to no sense. When Sard came back he wanted everything that he wanted on the market and this increased my overhead volume even more. However, once again, it sold in fits and spurts. I also learned a lot more about various modules that PvPers will want to have.
As things settled I also worked to build up a reasonable carebear front for non PvPers. I've had arguments with people over warpcore stabilizers and EC drones when they do not wish me to stock them and I feel that I should for the greater good.
Now that I am past six months I've started having things delist regularly. I admit that I am still terrible at remembering to check expired orders. What the expired orders are showing me is that some things are just not going to sell well enough to keep the ISK invested in them and the orders occupied with them. It is a hard decision with my full market concept. However, I have to look at who I sell to. I sell to a bunch of low sec PvPers. In general the base skill level that enters the area is going to be higher.
In a perfect world I would be able to stock everything. I don't live in that perfect world. It is just me. I have several items that just do not move. They delist every three months. They occasionally sell out but in general I do not see them sell.
This is mostly T1 modules but it also covers some less used T2 modules. What it has shown me is the scope of my market. While I have the occasional low level or unskilled player wander into the area for the most part very basic meta modules do not sell across the spectrum. Passive tanking is more popular than active tanking for PvP. Active tanking happens but it is a niche and I keep lightly supplied in the common uses. Things like shield boosters are almost never purchased. I do not think I can justify holding and stocking items that do not sell for months at a time with my limitations.
Fitting modules are always important. They sell sporadically but people find that they need them. All the meta DCU and the T2 DCU except for the meta 0. Various fits require various meta Damage Control Units. Meta 0 T1 guns are rarely purchased from my store. Long range guns except for artillery are almost never purchased as well.
I won't thin out everything that has a low volume. Large guns for instance sell very slowly and sporadically because there is not very much battleship action going on. However, Meta 4 large guns sell a bit more often than T2 due to the lower skill requirements. Therefore I am tightened up to Meta 4 and T2 guns only except for ganking equipment. Also Meta 0 fitting modules tend to sell.
I stepped into the mining equipment experiment fields. I've learned that Procures sell well. Retrievers are meh. T1 mining lasers sell. T2 mining lasers don't. Strip miners sell okay. Ventures sell but not in high or steady volume.
The orders I thin out can be used to bring in more rigs. Rigs are an interesting market. They are important but most of us do not wish to rip them out once installed. This stops the rig market from moving quickly the larger it is and the less common the ships are lost. Because of that I keep only tanking modules for large rigs except common non-tanking large rigs that THC and 7-2 uses.
For medium rigs I've expanded into buffer tanking rigs, resist rigs, dps rigs, and fitting rigs. I also added in the active armor repair rigs because I consider them a set with the ancillary armor repair module. I do not stock other more active tanking rigs.
Small rigs are the most diverse. Here is is tanking, resist, dps, fitting, and other. Things like speed rigs, probing rigs, and hacking rigs are all very common. It creates a pyramid shape to the sales pattern of the store. Spread out for frigates and narrow up to battleships.
For the most part you can never go wrong with stocking a strong frigate market in low sec and null sec. In high sec, I don't know. I don't live there. I see more large ships than small for instance as people rush to their goal points as fast as they can.
The last area of purging is the ammo market. I stocked selections of basic ammunition to see how it sells. Some areas sell well. People to run missions in low sec. Other areas move slowly. The slow movers I have pruned back. These are mostly in hybrid and projectile ammo. Basic missile ammo sells well. Basic crystals don't sell at all except for large standard which is commonly used. This allows me to focus on faction and T2 ammo which sells well due to its common use in PvP.
I do take a moment to point out that this is low sec focused sales. Milage will vary with other locations in space due to the inherent need of different ship types.