If it ain't broke

[Alan Klein]

I think you didn't understand what I described and John referred to. With Ctrl depressed you click on the dust spot and without  releasing Ctrl you drag from the spot to the desired source location. The tool doesn't make a guess, so there is no "guess spot".

OK I get it.  Thanks. 

The problem I usually have is when there is a second spot very next to the first.  It's hard to select the second spot without grabbing the first. Is there a way around this? 

[john beardsworth]

Kind of - use the H key. H stands for Hidden, so pressing H cycles between the various states. When there are lots of spots or it's a complex heal, I find it very useful to keep all spots hidden while working (though sometimes one needs to unhide them). The Auto view is my default as I can swing the cursor away from the image and see the current result.