If a buy offer with a price offer above market price is created then the percent number to be entered is negative.
This is somehow a double negation: market price - (- percent) = price of the offer
Perfectly fine to understand for a software developer, but maybe confusing for an average user that may not create or take such an offer.
I guess it was built with an assumption that people will offer trades that are profitable to them instead of the other trader. Which is currently most common scenario.
If the roles were to be reversed, you would have most offers with a negative percent.
I don’t know if that would be better, but it is certainly a valid UI debate.
Looking at this old thread Why All These Negative Offers? these negative numbers have already lead to confusion in the past.
A simple UI improvement would be to indicate the sign of the number as text (above/below) market price and as radio button when creating offers. Internally the number can still be stored as a signed number.
The price is subjective and therefore I wouldn’t use the term profitable in this concern. Paying 1 percent above market price compared to several percent at a centralized exchange/broker is still a good deal for a buyer; maybe less for a trader, but there are several use cases for Bisq I guess.