This is total BS, IMO. You can't breed a 1000 gram female ball python, so why would anyone cool one? I would ask for at least some compensation for this--the breeder did not FEED the snake! 700 grams when you were expecting a 1000 gram animal? Ridiculous!
When my snakes are off feed, they usually only lose about 1 or 2 ounces per month--more like 60 grams, rather than 100.

I would say the breeder didn't feel like feeding the snake. And no, there is NOTHING normal about this at all.