Ok then let me tell you why this is dumb.
Bait and Confuse Victims: You should not be flagrantly refusing to be mugged because of your OOC belief that it's a whiteshirt. Roleplay it. Assume its a real guy. I've never heard this in my entire time as staff, someone going "Well I thought it was a fail mug because they didnt have expensive clothes". Usually people who are mugging people are wearing nothing or wearing clothing store outfits, both of which you would assume is a new person if you aren't aware of their identity. Having clothes on doesn't change the dynamic. But, more on that -
Risk - They are risking their character. Not wearing expensive clothes *to a mugging* doesn't actually mean anything for the risk. Unless they gave their clothes away *prior to the mugging*, which is actually still allowed so long as it doesn't come back to them. It really doesn't matter.
None of this actually matters. If it's a fail mug, it gets reversed, we get the items back, if they're unrecoverable because its on an individuals person and they refuse to relinquish, we pk the char and just spawn you new clothes. You taking a decided risk to shoot at someone during a mugging is just short sighted, low IQ behavior and completely on you. Don't shoot at someone during a mugging on the chance that it's "A new player, and it will be reversed." If you're going to take that gamble, you're going to lose that gamble.
Literally everybody who gets mugged ever immediately thinks its a "Mugging char" or a "Fail mug", as noted by every single ticket that is made in the aftermath of a mugging. Every single one. "Can you check if this is a mugging char, he had shitty clothes on" or whatever, the exact same logic you're using. But those people aren't dumb enough to risk their character on a hunch because of a perpetrators fashion choices.