How do i email a customer that i want to send an offer to?

[caldreamer]

You cannot do that (considered spam).   EBAY decides which "select few" customers you can send offers to.

[albertabrightalberta]

@orbieone23-2 

If someone sent you a question, you have the option of sending an offer at the time you're answering their question. 

If it's just a random watcher, you can send an offer through the seller hub: Listings eligible to send offers

You don't get to choose who the offers go to.