You are being compared to the house brand
On a pure marketplace, a buyer compares third-party sellers with each other. On a department store marketplace, they compare you with El Corte Inglés itself.
That is a harder comparison and a more revealing one. The buyer already trusts the retailer; what they are working out is whether buying from a partner seller inside it carries the same guarantees. Every hesitation they have is about you, not about the platform.
Reviews are the only thing on the page that answers that hesitation in your voice rather than the retailer's. A partner listing with a solid body of reviews reads as an extension of the store. One with none reads as a stranger who has rented a shelf.
Breadth means no single timing rule works
El Corte Inglés spans categories that behave nothing alike. A seller shipping small electronics and a seller shipping homeware are solving different problems, and a seller shipping both is solving two at once.
Anyone telling you there is one correct number of days to wait before asking is not paying attention. The delay has to follow the product: quick for consumables, patient for anything that needs installing or wearing in. On a marketplace this broad, that is a per-catalogue decision, made once at setup.
Spanish buyers, Spanish message
The message goes out in Spanish, written to read like a person wrote it. This matters more on a heritage retailer than on a discount marketplace: the buyer's expectations were set by a brand with a century of service behind it, and a clumsy translated template undercuts you against exactly the standard you are being judged by.
What Merita does
We read the delivery event on each El Corte Inglés order, apply a delay suited to what was actually sold, and send one message in Spanish through the marketplace's own buyer messaging asking for an honest review. Nothing offered in return, one message per order, and any order carrying a complaint, refund or open return excluded automatically.