Nothing to do with the seller allowing, there just needs to be enough on chain liquidity available on the coordinator you have chosen.
Discussion
Thanks! I guess the robosats documentation will explain what a coordinator is, so I'll read that.
I don't remember choosing anything besides a robot identity and a seller. How do I see which coordinator I've chosen and how much liquidity it has, before trying to buy?
What do you mean by "coordinator"? I can't figure out what you're talking about.
Coordinator is where your trade is ‘hosted’. With the latest RS release, there are multiple coordinators in the federation – when you create a trade you can select which one to use, ex. Experimental (original RS), Temple of Sats, Satstralia, The Big Lake, BitcoinVeneto are the current choices.