I can't answer your question in a specific way, unless I know not only what coin you're selling, but also what coin you are buying. But generally speaking, there is no single price for a cryptocurrency, the prices vary across exchanges for a variety of reasons. To see how extreme this can be, look at current prices on various exchanges for Steem Dollars (SBD): https://coinmarketcap.com/currencies/steem-dollars/markets/
We therefore have to make decisions about which prices are actually valid ones. One reason a price may not be valid is if most people are not able to trade on an exchange offering a price at variance with the rest of the exchanges. This can happen if the exchange disables deposits/withdrawals or if they only allow citizens to trade on their exchange (this is true for Korean-based exchanges, for example). Price aggregators like coingecko and coinmarketcap try to compute a "blended" price to account for this price variance and we do something similar, but we each use different techniques, so our decisions about a "fair" price will sometimes differ.
Help, steemit seems to be crashing. 3 top devs just resigned. Worse though, I can't sell my steem on Blocktrades, the only exit for us all, because steem is "under maintenance". Was there any explanation somewhere, like a post? How long do we have to wait before we can sell or buy? Who put this block on blocktrades? This really looks very suspicious.