I have some trades with extreme spread ranging from 20-65%. Most of my spreads are in the range of +/- 0-1%, but I don't know how to deal with the extreme outliers. The most extreme trades are USDT/TRX, USDT/XDN, but some of the trades with a spread in the range 5-20% are also more mainstream currencies like USDT/ZEC and USDT/XMR.

Am I supposed to correct for these somehow, or do I leave them alone? Could these extreme values explain why my average purchase price of USDT is way off, like almost 350 regular USD?

If I should correct for this, how would be the best way to do this? Where could I find the "real" value of the coin in question?