If you're a domain name investor you should be listing your domain names on Godaddy's Premium Listing platform. I sell 5-10 domains through the listings per month. There is a difference between an auction listing and a premium listing and I'll explain that below.
A Premium listing is setup in your domain manager under "monetize", when selecting a price keep in mind that Godaddy will charge you 20% commission fee. These premium listings are then displayed to the millions of searches that are being preformed on Godaddy per month. If someone searches for your term or a similar term of your premium listing they will be prompted to purchase the domain. Once someone purchases your domain through premium listings you will receive an email stating "Your Premium Listing Just Sold" with the domain and the date. The buyer will typically have the domain automatically transferred into their account within a few hours and you'll receive your payout in 6 days.
A premium listing is also displayed in the the auction section of Godaddy automatically. If a buyer finds the domain through the auction search and makes the purchase you will receive an email stating "your domain, xxxx.com, has sold." The main difference here is typically for the buyer since they'll now have to wait 6 days for the domain to be transferred to them, once the funds have cleared on the 6th day the domain is automatically transferred to their account. You'll receive your payment in about 2 business days after that 6th day.
Auction listings are completely separate in the Godaddy system. These listings typically follow the information I posted above, the buyer will make the payment, the funds are held and on the 6th day the domain is transferred to the buyer's account and the seller will receive the payout within 2 business days.
Whenever possible its always easier to have the buyer purchase the domain name through your premium listing since they'll receive the domain sooner and you'll receive the payment quicker. One thing I do is to send the buyer a link which will automatically search godaddy for the domain and will display the premium listing for them.
Here is the link I use, remove mydomain.com and insert your domain, this will bring them directly to your premium listing.
I am guessing you are talking about instances where your customer has contacted you before purchasing the domain name?
@dirtmaker Not necessarily no, only the latter portion of my post with the link would be what you would provide to your customer. The rest of the article is simply the difference between the two of them.