If I buy something off Vinted and the seller is attractive, I flirt with them via messaging. Body count is four and rising.
I agree, and I'd never flirt in that setting, even if I weren't married.
However…
People using Vinted are usually buying clothes for themselves. So Fessor is probably flirting with people of the same sex. Since Vinted is mostly about women's clothes, there's a good chance that Fessor is a lesbian. Does that change anything?