Since we have a constant influx of new players, I figured I'd throw out some tips on purchasing new team members from the tradelist, as I haven't seen a good guide to it.
So you're new here, and you're looking to help expand your team. The first thing I would recommend is posting in the forums for a loan from an experienced team. The team will invest money in you, and in exchange you receive a (usually) young, future star for a to be determined number of seasons. This is almost always the best way to start out your first few seasons, as it can get you a lot of purchases without ever worrying about money.
Now let's go forward to when you're ready for the tradelist. I almost always will recommend buying for the future. Sure, that 84 avg selling for only 15k might look nice, but if he's aged 33 he might only last for a season or two. If that happens, you just wasted all of that gold on a player that won't give much return to your team. That leads me to my second point here: Buy a player that you can get more in return from than what you invested in him. There is a time and place for almost every purchase, so be aware of what your potential is for the next 2-3 seasons and what a player could do for your team.
I will give an example of this. If your team is at the Iron or even Steel level, you have quite a ways to work up before you get to the big leagues. At this point, buying a high level, old player would be a mistake. They will retire by the time you make it through Bronze, and then you'll be starting all over again and with an even more difficult ladder to climb. Instead, invest in a younger player that you can take with you through the seasons until you make it up to Gold or Honour.
You will see plenty of high level players being sold. You should hold off on these purchases until you are at a level where it could make a difference for you. A player that is 88AVG and 32 years old might be worth the 50k investment to an Honour league team that is fighting for the top 3 places. But for most other teams, that very same player would really only be worth about 10-15k. They just won't bring in enough wins over time.
Moving forward, you found yourself a strapping young 18 year old. What next? Well, you should of course be looking for the key stats of their position. Hopefully you're already 2 or 3 seasons in and you have an understanding of this. If not, there is a simplified guide that you should take a look at. Even by that, managers may dispute over certain stats, but most agree on which ones are among the top 3 or 4, even if they dispute their order. So by this logic, you obviously would be better off buying an 50AVG chaser with above average accuracy and agility over a 55AVG chaser with low accuracy and agility but high morale and charm.
Finally the buying part. I alluded to this earlier when saying that you should find a player that gives you a better return than your investment in said player. You want to get this player for the right price, and don't want to get in a bidding war with other managers. Every player has a right price, so make sure you don't get hung up on a player and spend too much on them. If you're reading this guide, you're going to want to avoid players 31 and up. These players are no longer really developing, and could retire soon. Easy example: An 81AVG, 31 year old is really only worth a max amount of 15,000G to you. I would subtract 3,000G from that amount for every additional year after 31. Even a 90AVG, 31 year old should only go for 30-40,000, and that is a bidding war I would reserve for Gold and Honour league teams. The most expensive players you might look at are ones that are 85AVG or higher, while being 25 years or younger. These are players in their prime, with 5-6 seasons to develop. However, they are valuable to all leagues, and it isn't uncommon to see 60,000G or even much more being spent on one of these players. My recommendation, play your cash safe. Find a 50AVG, 18 year that you can snag up for 8-15K. You don't want to be spending much more than that on a single player, you have an entire team to build.
Well new players, I wish you the best of luck. Remember, the tradelist is always being filled with new players by other managers. Don't fret about buying one that's too expensive just to get that position filled. Find the right one for the right price.