You acknowledge that the quoted Buy Price Conversion Rate may not be the same as the Sell Price Conversion Rate at any given time, and that Coinbase may add a margin or “spread” to the quoted Conversion Rate.
If that's in the GDAX TOS, it's an unnecessary disclaimer. The best Bid and Ask are by definition not the same price, otherwise one or the other order would have been at market and matched against the other, and there is always a non-zero spread between the two.
I like how they say "may add"... haha, they always add it! I assume they're talking about the GDAX order book but if you watch the live coinbase price data on tradingview.com and try to buy bitcoin on casebase at the exact same time, it's always a little higher on coinbase.com (about 0.5% higher from my experience). I wouldn't mind if they weren't also charging an additional ~4% fee on top of that.
Definitely more than a wire transfer, but I'm not sure where else to buy with a credit card at a lower fee. Buying instantly at a known price is much better than a wire transfer that comes through in 2-3 days -- who knows what the price will be when it comes through!
You acknowledge that the quoted Buy Price Conversion Rate may not be the same as the Sell Price Conversion Rate at any given time, and that Coinbase may add a margin or “spread” to the quoted Conversion Rate.