Yes really it is not big amount for me. Just for testing only i have done small trade. Whether he is genuine or scammer.
I dont think you are getting the point. 50$ might seem small to you, by rest assured it is not small to every other user in the world. Heck in 3rd world countries 50$ is worth of one good meal and thus you should never demean any denomination of money as to big or small and reason yourself for that.
There is not need to "test" someone.
Do you test whether a hole belongs to a rabbit for a snake by putting your hand inside and trying to reach for it? Or do you call someone who is certified with animals and use their help to check the hole? I could give even more dirty examples but lets now talk about that.
I might seem to be joking but this is a serious thing. The marketplace section of this forum is filled with scammers ready to pounce on users like you and scam them. They have no morals and so you have to be careful.