Why don’t you ASK? Havent you ever been asked “Would you like fries with that?” I mean, its only the world’s most common upsell (ok, maybe the most-common U.S. upsell…).
ASK. Dont say no for the customer. That’s their job. Your job is to remind them of what you have that they want, or to a lesser extent, need.
I can’t tell you how many times I’ve left a store, driven down the road and thought, “Damn, I forgot *whatever*”.
When you and your staff don’t ask (and do so IN CONTEXT and SINCERELY), you might be costing me time and money. Ask smart questions, make smart suggestions and help me out. You’ll stand out in a crowd of lost business souls.