Why so many different BTC prices on different exchanges?

Every exchange has different price and the difference is often really big.

 

There will be a discount if the exchange is questionable in some way. Low liquidity/poor spreads, ease of funding (getting fiat in esp), some exchanges trade against tether which is a whole nother can of worms, some don't allow US customers, ones domiciled in or mostly serving Asian countries have driven certain crypto higher than elsewhere. Recently coinbase is the highest which I guess reflects its the easiest to trade on and get money in and out of.

Feel free to arb

 

I was checking Coinbase, Bittrex, Bitstamp, Poloniex, ...

Coinbase was always the highest ...

 

Coinbase you can trade USD fairly easily. Bittrex is USD-tether only so zero USD traded markets. Bitstamp is run out of Slovenia/London. Poloniex also has no USD trading...only tether.

Kraken has USD and Euro trading but their website crashes on every other click. Takes 5 tries to submit a trade.

If you are reasonably savvy, don't trade coinbase. Use GDAX...it's the same company and funds on Coinbase are available on GDAX. No 1% commission and zero transfer fees.

 

Try and figure out which one isn't a bucket shop (or a leaky bucket for hackers).