In a perfect world other managers would research your team, decipher your plan and offer to fill your needs. And that can happen, it's not all that hard, but trades can get done in a lot of different ways.
When i first started I didn't like the unprompted trade offer, without any e-mail contact, but I realized that it can be useful and effective if done right. My point is that if you take the time to figure out the other guys needs, and it's usually easy to do as in PB most teams are either contending or rebuilding (more so than in MLB where teams straddle the fence for PR and attendance reasons) then you can offer something fair. Anyone who is trying to rip people off will fail regardless of method, but I also think too many GM's think they're being ripped off to easily. We all overvalue our own players, so just say no, or give your reasons why not. Communication is the key.