Most shops keep the case in one place, the web store in another, and the buylist in a group chat, then spend Sunday night making the three agree.
modu is the single source of truth for your stock. Everything you take in lands here, gets priced here, and is sold from here. Your case, your storefront, ManaPool, and Discord all read and write the same record.
A single card off the counter, a ManaBox CSV, or a graded buylist haul. Log it once and it's for sale on every channel.
Your case, your storefront, ManaPool, and the Discord bot all work off the same count, so a sale on any of them updates the rest.
Set your rules and modu follows the market inside them. There's one number per card, and every channel quotes it.
Customers build a cart from what you actually have, review it, and submit without leaving your server. You get a DM the moment it lands.
Players get quoted from the buy prices you already set, so an offer arrives priced and ready to accept. Every card you take in lands in the same inventory.
One system, one bill, and it only costs you when a card sells. No minimum, no monthly fee. A slow month costs you almost nothing.