The part of marketplace integration that causes the most trouble is stock. The reason is simple: stock is held both in your system and on the marketplace, and there's a lag between them.
01. A Single Source of Truth
The single source of truth for stock must be the ERP or the WMS, never the marketplace. The value on the marketplace should always be treated as a copy and regularly overwritten.
02. Update Frequency
Sending the full list continuously through the day burns API limits. The right approach is to push changed products immediately and the full list once a day. That gets you both speed and consistency.
03. Safety Stock
For fast-moving products, sending the marketplace a figure slightly below real stock materially reduces cancellations caused by simultaneous orders. The margin should be set by turnover rate.
04. Pulling Orders
Order retrieval must be repeatable: pulling the same order twice must not create two records. The marketplace order number should be used as the unique key.
05. Writing Status Back
Shipped status and tracking numbers must be written back to the marketplace promptly. Late writes damage your shipping-time metric and lower your store score.
06. Monitoring
The last run time and error count of synchronisation jobs must be visible on one screen. A job that silently stops loses sales for days before anyone notices.