I guess the merchant you traded with was using Floating rate. There are two types of rate when placing an add on any exchange 'Floating rate and Fixed rate' and you were supposed to see a pop message before placing the order which give you the window to decide either to continue with the merchant or not and it's obviously captured in your screenshot with the option to cancel. I have experienced this on a good number of exchanges and I don't see it as scam. It's a good thing you shared cos it has provided an opportunity to enlighten users further.
You are right with your objection but I want you to know that most Nigerian market used a fixed rate, they don't allow Nigerians to use a floating rate because since I have been using exchange p2p even before coming to this forum, I have never click on selling adds and then see a pop message for option of fix or float price, there is nothing like that but perhaps Bitget exchange allow such option for Nigerians but this is very bad because Nigerians are opportunist that will used such ignorance to manipulate sellers, not a good options to be honest.
Another thing is that the government will have more reason to ban p2p because this looks like scam and a lot of noobs who understand how this works will be cheated, sell at lower price and then buy at higher price, such behavior will tend to increase the price of dollars against the Naira and this is what the government dislike because it's kill the valuation of Nigerian currency.