Why can buyers send a second, lower offer mere moments after I accept their first?

I’m a Depop veteran who is new to Vinted. These messages are a couple minutes apart. This is just not how negotiation works in any sane world!

If they make an offer that I find acceptable, I accept. If they make an offer that I find unacceptable, I counter or just decline. Why should they get to go lower one minute after I accept the price that THEY named? I can’t change my mind and go higher after sending an offer.

I left a detailed, 3-star review of Vinted on the App Store (for more issues than just this) and I encourage others to do the same.