I've read that artists should expect to discount up to 25% and this would occur during negotiations with an interested buyer. However, I think this bit of advice is a carry over from the days when artists depended on galleries to sell their art work. Negotiations might also work for studio artists who have people dropping buy to visit and buy expensive art.
Joe Paquet, a well-known landscape artist, lives in my area. He prices his work in the $19,000 and up range, and he includes prices on his websiite. He also holds special events for collectors, during which he offers a discount on specific pieces. He may also discount on a regular basis (I don't know). My point is that he is open with his pricing.
I can think of several reasons to avoid having to deal with email requests and negotiations. The biggest single reason is payment. I get paid on DPW before I ship a painting and I don't have to worry about whether or not a check will clear or a credit card has available credit.
I agree with David and others that the buy process needs to be easy. For this reason, I also tend not to use the auction route. Auctions may work well for some people, and maybe some people do enjoy the game of buying through the actions.On the other hand, waiting several days between bidding and buying (or being outbid) can be very annoying. What I've observed here on DPW is that auctions are a way for people to buy good art CHEAP. Super cheap, when people start their auctions with $1 and pieces are sold for a small fraction of their value.
To avoid rambling, I'll conclude by saying that I would not use "contact artist for price." In my opinion, open pricing and PayPal pre-qualify buyers and remove barriers in the buy process. If they're not willing to pay the stated price, they move on.