I rarely contact end users as I think spending more time buying the right domains in the first place has better results. Instead of spending hours emailing people on okay domains spend all that time scouring drop lists and then your inventory will be stronger and you can kick your feet up and watch offers roll in naturally on their own each month. I don't sell as many as the proactive guys here but I don't need to as it's not odd for me to go well over 1000% return on investment. One tip I would give to eliminate the back and forth emails of how much, how do I pay etc... is to generate a list of emails for end users for your domain then start an auction listing at Bido, Sedo, etc... set the reserve at the lowest price that makes ya happy and then email or call all the end users on your list and whether the domain sells for $100 or $10000 you did the best you could do by inviting the perfect end users to the listing and if it sells for less than you expected really can't have any regret if you invited the top dogs to the listing, plus an auction throws a sense of urgency on the bidding and usually increases value if at least 2 people you contacted fight it out. An auction format has the best chance of increasing value, you just gotta invite the right people to your listing.
Sedo=Auction Format
Bido=Auction Format
Afternic=Auction Format
Rick Latona=Just changed his newsletter to Auction Format
etc...
another tip affiliate code the link you send to end users which can be done at Sedo, Bido and Afternic so if one of the end users you contact buys then they are tagged as your affiliate for that purchase and any future ones as well.