The price you see at BUX Zero is coming from various exchanges and Liquidity Providers and may contain a markup. The bid and ask could be 98 and 102 on exchange A, but they can be 101 and 103 on exchange B. The prices on various exchanges are usually close to each other, but rarely the same. Some exchanges/brokers also show a ‘midprice’, where they take the bid and ask and calculate the average to be the price.