Hello Evrybody ..

Im thinking of starting a new business in my city .. a BTC store .. where im going to sell BTC,
But Simply .. if i sell 1 BTC for 596 $ .. and the customer goes home and try to use it .. then he found that its worth 570$ .. Surely he gonna think this fraud.

like before 10 minutes .. the price was 596 $ .. now its 617 $

how i can let people but BTC's while it has no stable value in the market .. how we can solve this ? .. or What do you suggest in case of my idea ?