Hello.
I don’t know if it has been suggested, but anyway.
So, the Trading Post can calculate the amount of gold needed for a specific amount of Gem.
Now, why isn’t this possible with real life money? If I only want 200 gems for a Hood, either I spend my gold for an exchange (golds that are already hard to get) or I pay 10$ for 800 gems… Of course, I could spend the 600 remaining gems in other things, but that’s not the point, I shouldn’t be forced to pay for 800 if I only need 200, or 20$ if I only want 1000 gems.
It’s like if I went in a clothing store and only wanted a pair of jeans, but was forced to pay more and select other items as well whereas I only wanted a-pair-of-jeans.
So, tl;dr: Allow us to choose the amount of gems we want to buy instead of giving us specific amounts.