I've bought over 50m from usfine. I've used them for a long time they are pretty trustworthy......BUT
The only thing you have to watch out for is that your getting your money's worth...One time i bought 10m and had 2m on the account, when they said they were done i had 10m so they really only gave me 8m but i paid for 10m. Yeahh it's not that much but no one wants to get ripped off like that.
Other than that they are legit and pretty fast with their shit. And they always have some kind of discount code for you to use
Even if you want like 2-3% off and can't find a code talk to the support team and say your looking to buy whatever and just talk to them about it and get info on it and most the time if you say you might later they will give you a 2-3% off