If you have a good pet store or pet supply outlet try to shop there, there is a trick however. Somewhere on the package of the thermometer itself it should say where it's made, if it say's made in CHINA try and pick one that is made somewhere else. They have better and more choices than Chinamart and then you can rest a little easier with a product you can trust to accuratley give you the info you need for your hatch to be a maxium success.
If you still have the receipt and it's been less than (??1 week? 2 weeks???) you can take the receipt back and they will refund you the difference. I have several of those thermometers and they work just fine for me.