But why wouldn't they just use someone like bitpay, or have a similar setup that the coffee shops and bars that accept bitcoin use?
EDIT: If it works, then that is great that you have gotten small businesses to accept bitcoin. I am also curious as to how you would account for changes in price.
because businesses still think bitcoin is the shady market of pirate, drugs, and scams. so they are unwilling at first to want to link their business bank account to such perceived entities. its only when real people start paying with bitcoin, that a merchant then goes and investigates its potential, and the deper truth. until its actually part of his business or something he is interested in, he has better things to do then spend hours researching it all just to learn if bitpay is legit, or shady.. remember not everyone is a bitcoin community member that knows which businesses are legit or shady..
so by sliding in the bartab, where the merchant does not have to "trust" that FIAT money will arrive AFTER a customer has walked out the door with stock, they merchant already has it. then as bitcoin is part of his business and bringing customers to him. he will then be incentivised to research bitcoin beyond the 20 second news item on TV. as he will want to find ways to cut corners and save a few pennies or make more profits..
again the bartab is just the opener, the foot in the door, the toe in the water, the beginning to a merchant accepting and understanding bitcoin
as for how i account for the change in price..
just like everyone else including bitpay. i have a website that is a live price checker.. say now bitcoin was $600 and my spot (commission was 1%) the merchant wanted to sell something for $60 my website would show a price of 0.101btc.
if the price in 10 minutes time went to $650 and the merchant had another customer with a $60 purchase. my website would show 0.09323076 (but my website usually rounds it up to 4 decimal places just for easy use 0.0923).
and in both cases the merchant then takes $60 from the bartab once the website shows that the bitcoin amount has been seen on that address. and yes i accept 0 confirms, just like bitpay
basically i do everything bitpay does with its pricing calculation, but i do it using a single QR code that the merchant can laminate or velcro to a display for customers. and i pre-pay merchants (bartab)..