The honest version of "does it integrate with my software." These are the systems this industry actually runs on, and what each one means for a build.
Lightspeed / Square / Shopify POSPoint of sale
The system of record for sales, inventory, customers and increasingly the online channel, all with accessible interfaces.
Inventory and purchasingBuying
Reorder points, vendor lead times and open purchase orders, which in most independent stores live substantially in the owner's head.
Vendor and supplier orderingSupply
Wholesale portals, sales reps and trade shows, with pricing and terms that change and are rarely tracked systematically.
Customer loyaltyRetention
Loyalty and customer data that most stores collect and almost none use for anything specific.
E-commerce and marketplacesChannels
An online storefront sharing inventory with the floor, where a sync failure sells something twice.
Email and socialMarketing
Where the store talks to its customers, usually the same message to everyone.
AccountingFinance
QuickBooks alongside the point of sale, with margin by category rarely visible without work.