I have three suggestions more:
1. How much will requested model be useful also for the others
Modelers usually want their models to be used in more maps if possible. This way, in case your map/project die, it can be still used by other people. Good example are starwars models, even though SWTJ died, still many people use those models. Requesting a random character from the most obscure anime, which only the most hardcore otaku are aware of, greatly decreases usefulness of the model. So generic models are in the end more useful than strictly based on other thing.
2. Try to get the best pictures from different angles (this is basically an addition to Xlightscreen first rule)
A single, blurry and from awkward angle snapshoted picture of the object won't help the modeler too much. Ideally would be like the way vehicles are shown in Red Alert 2 installation (i'm sorry if you don't know the game), but it's hard to find that kind of pictures. So, if possible, for example, avoid to throw just an anime character picture (especially if covered by other characters and objects), try to find him also from other sides.
3. Don't request too many models
If you're going to request like 300 models, it is more likely that you won't be taken seriously and your request would be done even for one model (unless you have in mind that movie

)