give your price if you have any in mind or ask for theyr best offer, and go with an escrow company if you reach a deal.
If this person is asking for a valuation of the domain by a third party just do not respond anymore, because is an old scam trick.
best of luck
You should give them a price since you reached out to them first. Asking them to make an offer will make you come across shady in a way. Personally, I haven't had good outcomes from reaching out to end users and then asking them to make an offer.
If they reach out to you first then that's completely different.