I wanted to buy this watch from someone, he said he's been using this watch for 2 years. Also, he said this is the v5 JF Factory 15703.
My questions are: How does the watch look? What are the flaws? Is there any instant callout flaw? and is the watch really from JF?
I think you are asking the wrong questions.
1. Be it JF or any other factory, EVERY diver rep is flawed and can be called out if you know what to look for. No exception for the watch you showed. It is very flawed, and far from 1:1, so manage your expectations accordingly. Don't expect to pay $200-300 and have a rep which is perfect in details.
2. I do not know if the watch is a JF but it does not matter where it is from, if you expecting a 1:1 rep nobody can call out, this is not the watch to buy. It could be a JF V7. I do not recall a JF V5 but someone else with better memory or knowledge than me can answer you better if there is a JF V5 SS diver.
Get what you like, and wear it as a novelty. Unless you are wearing the watch to impress someone else, you do not need to worry what anyone else thinks.