Faiien

They say that there are thousands(or is it hundreds of thousands) of Galaxies out there and that most of them indeed are galaxies. I'm wondering how can they tell for sure if they are galaxies or not? Main reason I'm confused is this, if 1 very distant object(star/galaxy) can through gravitational lensing appear to us for example as 10 separate sources of light, etc. I guess to rephrase that, taking Lensing into consideration, how do we know which are really stars/galaxies?