The venue can absolutely put pressure on a promoter to move a show, seen it happen many times. Unless the headline act is bringing trucks of pa, lighting and backline, then the venue has to provide pa, lights, catering, staff, security, stage crew, house techs, etc. all as part of the deal, If the headline act is bringing everything, then the venue will have to pay a production buyout, that is added on to the band's guarantee.

If a 15,000 room is only going to get 3000 people in, that's a huge loss for them in the areas they would normally rinse everybody. Drinks, food, parking... plus their cut of the merch sales is going to be considerably smaller. Just about every venue takes a cut. Arenas 25% minimum, some theatres too. Most merch splits (even on artist sells) are 80/20 or 85/15. There are still a number of venues that don't take a cut. A lot of Live Nation venues don't (unless it's a venue sell). But even clubs will take a cut of merch.

Pulling a show will come from dialogue between promoter, management and venue. Management rarely want shows pulled...

Touring techs don't get extra travel expenses if they are part of the touring crew. They get their day rate, which is already budgeted for long before the 'boots hit the ground', so to speak. They don't get a rate for show days and a different one for travel days. Unless they are working at baby band level.

Regardless of sales, the band's guarantee is always met, if they a play a half full room, they still get their money. Of course, no one wants to play half filled rooms, but they get their guarantee regardless. I very much doubt Sammy's fee is chump change.