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1. The CPU tends to make rather insulting offers and counter-offers. Generally speaking it's easier to make trades with teams that are struggling as they have more incentive to make changes. Also note that trade value comes down to a player's overall rating. If the total value of the overall ratings you're trading is equal to the total value of the overall ratings you're receiving (or you're giving up more than you're receiving), you stand a good chance of having the trade accepted. The interest bars for your players, indicating just how willing a team is to acquire your player, is also a good guide.
2. Players have hidden development attributes which determine their likelihood of developing. Aside from the monthly training through the Academy drills, player development takes place between seasons and comes down to the hidden potential rating. When you're drafting generated rookies in subsequent seasons, you can see their development potential while scouting them. What you do in the games and whether you give them time or not does not have an impact on their development. It's something we want to see in future games but to date development in the series doesn't work that way.
3. It is, but because real life salaries are used you're at the mercy of bad contracts that exist in real life.
4. It's a decent lineup for a rebuilding team.
5. The more games you win, the lower your pick in the Draft will be. Therefore if you're doing well, it might not be a bad idea to trade the picks away. Note that lower picks also have lower trade value, however.
6. The NBA utilises a soft cap, which means teams are able to exceed it but there are penalties and conditions. Teams can go as far over the cap as need be when re-signing their own players (in real life there's a luxury tax threshold for going too far over the cap but this is not represented in the game). Teams that have a positive value for cap space are under the cap, a negative value indicates they are over the cap.
In trades involving one or both teams being over the salary cap, the total value of the salaries from one team cannot be more than 125% of the salaries coming the other way. In other words, if you're over the cap and trading a player with a salary of $5,000,000, the player coming the other way cannot have a salary larger than 6,250,000 or smaller than 4,000,000.