I had Amber scanned, it cost me £20 by a sheep scanner, (they are supposed to be more accurate) she didn't shave her tummy, said it was unecessary and within about 5 seconds of scanning her she said, she is definitely pregnant another 5 seconds later she said 5 puppies. She then took the scanner off and said I will do a re-check and show you it all, she did and took a bit longer this time, about 40 seconds,

when she counted she could only count 4 puppies, so would only confirm 4, she had 5.

A friend used the same scanner on her tollie and was told 5 or 6 puppies and she had 9. She did say though that there could well be more as they can't always see them all, they can be hiding behind each other, or up under the ribs etc.
If you are having one scanned, my advice would be to find a sheep scanner they seem to be more accurate than vets, as they do it far more often. Don't use it for definite numbers, just for a confirmation of pregnancy and a rough idea of how many. I wanted her scanned as it was her first litter, I wanted a rough idea of how many, (I had a big waiting list

) I didn't want to up/change her food if she wasn't pregnant and there was so many things to plan, buy and get ready.
Good luck.