(1) How do we know our spread when enter a trade is a fair spread ??
I'd suggest having a secondary source open. This could be an MT4/FreeStockCharts and just notice the difference in quoted prices. Usually, it's a couple of tenths of a pip, and pretty fair.
(2) Is this real game of market analysis or just gambling ?
The sites definitely play more to the quick gambling side (make 500% profit and other such claims), but the truth is market analysis plays a big factor in many people's successes (including my own). Ultimately, in any market, I personally feel that you can never be 100% certain about your decisions. You just have probability, which you can put in your favour by doing your research (sentiment, fundamental, and technical). However, remember: probability does not equal certainty.
(3) What is the best trading platform with quick exception plus guarantee our money is safe ?
I personally have 24Option. I have just requested my first payout. I really have enjoyed the service, compared to another site I used. I don't get random phone calls, trying to get me to further fund my account. They provide a no-hassle, demo account (which doesn't contain an exorbitant amount of cash).
Ultimately, it comes down to personal preference, as many of these sites are cookie cutter creations.
Hope this helps! And good luck