There is well known option to notify Your friends and customers about the auction he/she might be interested in - "Email to a friend"
Some sellers do use it widely to advertise their goods, it is legal and convenient.
But there is a disadvantage: eBay limits the number of "Emails to a friend" sent per day.
To enlarge the amount of "Emails to a friend" use Your other registered identity,if You have that.
Or email Your friends directly via e-box and copy-paste the link to item You wish to advertise.