When you buy your new pets you want to get healthy ones. But not everybody offers only healthy mice. So you should have a closer look on the rodents taking the following items into consern:

1. Eyes
The eyes have to be bright and the skin round them shouldn't be reddish. Watering and wet eyes, small accumulations of matter, red or even swollen eyelids are a definite sign of an illness.

2. Nose
The nose of healthy rodents is clean and dry. If you can see there accumulations od does it look clogged or wet you can assume this rodent is sick.

3. Teeth
Rodent have two yellow-ish to orange coloured, straight incisors in the upper und two in the lower jaw which fit to each other if healthy. White teeth can be a hint on malnutrition. While you can see easily if incisors are too long or deformed it is difficult to find out if the rodent has problems with its molars. Such problems you will notice by lightweight because these animals often eat too few.

4. Fur
The fur of healthy rodents is fair, glossy, complete and has a consistant structure. But also fur of healthy mice can have gaps that result from scarves. But this isn't an illnes so you can buy it.
But avoid to buy mice with matt and shaggy fur.
A very greasy fur is especially for gerbils, jirds an jerboas a sign of false bedding, missing sand bath or false feeding. If it is the only problem, you can solve it with proper treatment and keeping. But though it's not a serious problem, have a very close look at such individuals!

5. Skin
Healthy skin is fair, smooth and without scurf. Is it scabby or dry or doesn't it look like it should in another way, it might point to an illness like parasites, dermatophytes or even malnutrition. Don't buy such rodents.

6. Anus
The anus of healthy mice is clean and dry. Is it filthy the mouse suffers from diarreah. It is definitly sick!

7. Breathing
Usually mice don't utter any audible noise. That's why you shouln't hear any noise when the mouse is relaxed.
Especially fancy mice often suffer from lung diseases. Then the mice literally seem to talk to you. This is a definite hint to an acute or chronic lung disease that may require a longer treatment.

8. Posture Healthy mice have a flat, consistent back and a relaxed posture. Does a mouse seem to crouch down or does it have a hump it usually is sick. Sometimes such individuals are simply very old.

9. Nutritional condition A healthy mouse's body has smooth curves, the tail is fair and you won't see any caudal vertebra. If a rodent seems to be very slim or you can see the caudal vertebra, it's sure that this individual has serious underweight. So it might be seriously sick.

10. Behavior
When you watch the rodents while their activity period they should be active as it has to be for the watched species. If an individual is conspicuously calm or moves without orientation, don't buy it. It is sick. Exaggerated cleaning and scratching may point to parasites or dermophytes.
Atypical tame rodents also may be sick. The same is with pets that suddenly get tame overnight. Take it as a sign of illness or near death.