I usually offer a bottle of water.
I used to tip for appliance delivery when I was younger and it felt awkward not to.
Fast forward through many improperly installed appliances, one that left water gushing out of my washer because the hose was attached incorrectly, a dishwasher that my husband needed to re-install, a refrigerator delivery guy, who I tipped $20, who ignored my pleas to remove a free metal piece off the top of the cart as he was moving it (thereby causing it to fall, damaging my hardwood floor: I did receive refund of $50 delivery fee for that one...) etc.
I pay the delivery charge, offer the guys a drink, and thank them as they leave. Works for me.