This year? Probably no bargaining; most gun shops I walk into can't keep a functioning gun under glass.
In a normal year, sans Banic, I typically make certain I know what it's going for on GunBroker (not listing for, but selling for) and start with a 75% of sticker price cash offer. That works half the time, and sometimes we land at 90% of sticker price.
If they act scandalized that I would impugn their modesty by making an aggressive offer. . . that's typically the last time I make an offer at that business.
To paraphrase Mad Dog Mattis, "be polite, be professional, and have a plan to walk away from any deal you'll regret later."