For the first time in PES history the achievements for MyClub have changed a bit so I've had to figure out how buying players via scouts from the auction house works. I assumed this achievement would be a pain at first but thankfully it's quite straight forward.
You need to buy scouts in auction which can then search for players to add to your team. So your GP currency (earn from various different ways like playing matches ect) is spent on getting the scouts and once that's done the player can be gotten for free. You can use up to three different scouts at once to pinpoint a certain player that you want. So for example somebody playing the game properly who wants Ronaldo in their team would choose a scout for Juventus, another for Portugal and another for Centre Forward. As long as those scouts were all 5 stars they would be guaranteed to receive Ronaldo.
That above example would probably cost a lot of GP though so I'm going to show you the player I bought to unlock the achievement which was a lot cheaper. Now as the achievement states it can be a Gold or Black player so I chose to save money and buy Level 4 star rated scouts as they can still get you a Gold player. Take a look at my purchase in the screenshot below.
As you can see my scouts were all 4 star and was able to pinpoint a specific player which gave me a 100% chance of getting the achievement. That's because Galatasaray only have 1 goalkeeper in their team who is over the age of 30 which guaranteed me the achievement. Without the Goalkeeper scout I may have still gotten Muslera as my player but it was now a 50% chance as there was another player in the team who was over the age of 30.
So my advice for getting this achievement is to first search specifically for two level 4 scouts that have a wide range of potential targets. My choices of Goalkeeper and 30+ gave me tons of available options at first but then my third scout was much more specific. What's great is when your in the auction house you can hit Y when on a selected auction to bring up potential players that can be signed with two slots available to add other scouts in.
What this means is you can keep looking on the auction house for Level 4 scouts at a specific club and test your other two scouts with this new scout (which you haven't yet purchased) to see if it will give you a 100% chance of getting the achievement. Once I saw the scout for Galatasaray would guarantee me a gold player I put a final bid in of 20,000 GP which was way over the first round bid of 4,000 GP. I was willing to do this as I wanted my achievement done but when purchasing the first two scouts you can risk it a bit more and try buying them on the cheap. The more scouts you buy the more variables you have to play with to increase the likelihood of having a 100% chance of getting a Gold player.
If anyone has any advice for better scouts to buy than mine then please comment and make suggestions. I don't believe mine were the best but it did allow me to get the achievement fairly quickly spending only 30,000 GP.