Look at you - dressed sharply, well-groomed, appearing friendly and outgoing with pleasant disposition, and likely to make a positive impression even before that first excerpt or solo is played. Surely they will have your contract in hand, except for one thing.
Your observers must look at that grungy tarnished war-torn instrument of yours. Rubber bands are holding broken spit valve springs and have corroded the plating badly. Your moldy valve guard protector has long since failed to protect anything. Dents dating back to marching band days are still visible dulling both your sound and your reputation. Those sticky valves from those inadvertent drops (that someone else did) continue to cause havoc with fast licks. Aren't you tired of glaring angrily at your horn while you pound the valves with your fist so they won't stick? For some reason you continue to struggle with all of these annoyances.
Slides tend to stay put while the bore of your horn has now likely shrunk from a Large to a Mighty Small. Several years of meal fragments line the lead pipe, and the mouthpiece bore once gleaming brightly now is full of craggy lumps. Who knows what has been lurking secretly inside your trumpet for months or even years?
If you play like an angel you are allowed to have a horn that looks like hell. But since most of us are fallen players of various degrees, we cannot afford the luxury of a cool-looking civil war relic for an ax. We need all equipment in top condition and ready for scrutiny.
Hey, clean the horn! Chem flushes work wonders. Your trumpet will play better and look better. Keep it that way. Its maintenance is a reflection of its owner. Impressions matter.