H/J shows base everything off of your trainer. Stalls/hay/bedding are all ordered by the trainer and then split out onto everyone’s bill by said trainer. I once broke a show manager’s brain by asking to be stabled with someone instead of having our trainer order stalls.
Communication from the show is generally only to the trainer.
Ultimately, it’s just very noticeable if you are amateur and alone. There’s no culture of allowing people to share warm up fences / stable next to their friends / share a hose / etc.
ETA: most shows assume you are a no show if you don’t show up until Friday afternoon to show on the weekend. The general culture of horse showing is that you send horsey on Monday or Tuesday with the trainer, and then the amateur client comes and horse shows Friday/Sat/Sun, after the trainer has done the horse in a few classes during the week.