If she is a mix, you won't be able to sell her for anything unless you scam some poor innocent moron, lol. Your vet will be able to tell if she is purebred, or, you may be able to find a Shih Tzu breeder local to you inthe paper or other public publication. Black IS a common color for Shih Tzus, but even so, if she isn't papered, you may STILL not be able to get much, if anything, from a sale.