They mention ipfs. Ipfs doesn't have a method of multiple people writing to one key.

How do they tackle this problem?

Edit: thanks in advance. I reached my time cap trying to find out

When a vendor creates a listing it's created as an ipfs file. Vistors download and seed them and we've added broadcasting so when you update your store changes will be pushed out to willing nodes preemptively.

Is there an architectural diagram or a protocol flow somewhere? I would love to understand the lifecycle of a listing.

In particular, I'm curious if in effect every client has to find, download, validate, and index every listing. And how far you expect that to scale.