While looking at some people's account on Z8 clan page, I discovered a simple method of telling how much crates each player bought (only works if he bought more than 50 crates)
In CrossFire's patch notes, it is stated that:
For every 50 Valentine's Day Crates purchased earn free rewards:
7 Day Kiss Grenade
7 Day Rose Grenade
7 Day Pink Muzzle Flame
(note that grenade prizes will not stack)
You probably would've noticed that the grenades' days wont add up together.
- I won 2 M4s + Awm pink with 530 Crates
(10 x 50 = 500)
As a result, you can calculate how many crates they bought with this formula:
(Number of Rose/ Kiss Grenades) x 50 + (0 - 49) = (Total Number Of Crates Purchased)
This wont be 100% accurate because the player would've bought 49 Crates and he won't receive any prize.