For stuff close to what I think of as market value w/ Best Offer enabled, I’ll just throw in what I’m willing to pay - I don’t generally message.
Sometimes there are items that are pretty overpriced though (maybe stale prices or unrealistic seller expectations) with offers enabled. I don’t want to come off as offensively lowballing the seller, so I try to usually explain a bit and point to comps to just make the case I’m giving a fair offer imo.