There are three things to look for when buying a pair of tweezers - starting with the weight; tweezers should feel comfortable and sturdy (too flimsy and they'll be difficult to control). They shouldn't be too 'springy':  a firm grip is required. And for ultimate precision, there should be no gap where the pincers meet. (That's why it's so important to keep tweezers in their carrying case, if they have one.)