When in doubt, ask for a feeding schedule sheet.
Most big breeders will have a record of when they ate. From that you can see for yourself if it's a picky eater, a good eater but slow grower, or underfed.

I never buy without a feeding schedule. It tells me when, how often, and what size they were fed, and also tells me the breeder keeps good records.

Most of the babies I've had have been between 200-600grams by the age of 7 months. Some eat less than others, I had a bumblebee that refused to eat much for the fist 4 months, and at 7 months was only 200. She started eating again and gained a lot in a short time on the same food.

Just depends.