So when normal store decide to receive bitcoin, he need POS machine? Maybe not? He just shows his printed static QR code image of his bitcoin address to customer?
My point exactly; you don't need a POS machine because you're dealing with cryptocurrencies.
But when we're dealing with the mainstream and micropayments brought by 3rd-party (
centralized) wallets, a POS Machine is a must for ease-of-access.
But are there no ways of store can also provide/include specific BTC amount as well with store's address QR code?
Or store should make customer know how much BTC they need to pay?
There's a way but the counter won't wait for at least one confirmation which is at least 10 minutes in situations like grocery payments or coffee shop orders.
So, it's not convenient to use Bitcoins directly for POS machine transactions.
You need to process the transactions off-chain like exchanges do.
with this, the users must trust your wallet/service like BitPay/coins does.