Hmm, good points... there would be a couple of ways around I think.

First off, I guess they could disable experience gain & loss from requested desynths. That would stop any assisted power levelling, and also stop you from losing/gaining points in crafts that you don't want to.

Then, they could either,

- Only allow people to request desynths when you reach a certain skill level (I dunno, say 90 or 95+? Maybe even 100?) Which would ensure a good success rate for most items, or;

- simply allow your skill levels to be seen by anyone requesting, and the success rates, and leave it to the customer to decide whether to risk it with your low rating, or find another (potentially higher charging) crafter!