I discovered flyp.me at the beginning, and I used it since then at least once per week, usually is pretty fast. Exchange rates are good but depends on the coin and the moment since this is something that's changing all the time.

Once I had a problem because Ethereum network was very slow, I sent an email and they answered me within an hour or so, and was also on Sunday, that doesn't mean that they will always respond that fast but it's a very good signal. Ofc they solved my problem and also kept the exchange rate they offered me in the first instance.

I'm also in the telegram group and I've seen some people had problems and the team always answers very fast. One common thing I see is when users send the transaction too late, flyp.me gives 10 minutes to send the transaction and starts counting from 0 confirmations, so in my opinion it's user's fault, also there is an option for refund address.

Also I remember they were ones of the first to implement segwit transactions.

So with no doubt they are trustworthy and I'm very happy with them.