I'm not sure if anyone else encounters this but my suggestion is to maybe implement a limit to how many times in a day, or some other amount of time, one person can challenge the same person.
I've noticed one or two people have been challenging me in the fashion arena a lot lately ( 5-10 times a day , everyday) and while I understand that is part of the game, it also drains me of my dollars really rapidly because those people have much much higher popularity rankings than me and so they always win large sums. It takes a lot of time and work for me to gain them back. To the person doing the challenging, it may be tempting and seem like easy money, but to the challenged it can be discouraging and ruin some of the fun of the game when they have to double their efforts to regain what they've lost. I feel like with a limit to how many times a person can be challenged by the same person, it keeps things fair and forces those people doing the repetitive challenging to find other people to challenge instead of having a "go to" person.