I can't say anything about what is usual (or "fair", for whatever definition of that). But if you want to be in a good position for negitiations, it's better to

I can't say anything about what is usual (or "fair", for whatever definition of that). But if you want to be in a good position for negitiations, it's better to make them say what percentage _they_ expect in return, and start from there. Asking you first is just a common negotiation tactic to get more than would be usual (especially if you're inexperienced with these things).