iPhone buying tips?

I am looking to buy iPhone soon. I looked all the net and there are a lot problems with i5... What should I look for? I am looking for Verizon i5 because it is factory unlocked and I stay 3-4 months per year in USA. Most of the people complain about WiFi is it that bad? It is one of the most thing why I am going to buy iPhone, because they have or had one of the most reliable WiFi. I had 3GS now Samsung S3 but I don't really like Android and I miss my iPhone :D. Some others complained about huge battery drains. I am looking on eBay and not so on Craigslist. Have bad experience with Craigslist :D Last year I bought 4S looking perfect everything good but when I tried to restore it, it couldn't finish the restore and when I went to Apple Store they told me that it has water damage. No way to return and no protection on Craigslist from frauds. eBay seems to be most protected from this point. Also I can buy some blacklisted iPhone and to loose a lot. What happens if I buy Verizon iPhone and restore it and try to activate it with foreign SIM (Local or Overseas). Or if I buy AT&T i5 and unlock it via site or eBay?
All ideas are welcome!
Thanks in advance :)