Hey, You asked for some first hand experience from the pros so here goes
Pokemon trading these days often evolves around RNG'ing, RNG'ing is the process where pokeomns IV's (Gives your pokemon extra stat increases) are made flawless (31 in every stat) and then there is EV training and i am sure you have heard of this one before but just to go over it quickly.
Ev training allows your pokemon to gain more stat increases in a single stat
For example, The highest ev's a pokemon can get in one stat is 250, but it is best to aim for 242, in this example i will be defeating 242 lillipups, which give +1 in attack. There are also items and the infection PKRS that allows your pokemon to earn ev's much much faster.
Was this good information or were you looking to hear about something in particular?