Selling fertile duck eggs to hatch.. . just keep them somewhere warm right?

[Kadjain]

I posted my fertile duck eggs for sale to incubate on CL and got a lot of responses. The first order I filled was 12 Khaki and 12 Muscovy eggs. A married couple came to pick them up and was looking around at my ducks and chickens. We were talking about the ducks and I asked "what kind of incubator do you have?"' The mans reply was "we don't have an incubator". So I asked "oh, do you have a broody hen?". He looked at me confused and asked "we can just keep them somewhere warm right, that will be ok won't it?"
Of course I told him "no" and explained why. Then I said "I can collect you another dozen while you get an incubator and set it up because I have someone else who is ready for eggs right now". His reply was "no we'll be ok, thanks" shook my hand and promptly left.
What is happening to those eggs.. ? I hope they're not sitting on top of a heater or on a windowsill in the sun.. .that would be too funny

 

[Judy]

I've read on here of someone's grandmother who used to hatch eggs in blankets in a corner near the wood stove, successfully. One or two here have hatched a (chicken) chick by keeping it in their bra for 3 weeks. You never know.

 

[Kadjain]

Well, good luck to them then.. .