Fortunately,after doing my homework,I found this thread https://bitcointalksearch.org/topic/offline-transactions-and-bluetooth-278237 where Andreas Schildbach answered everything in detail,right in the first post.What surprises me is the method was introduced way back in 2013 and not many use it yet.
OP,mind adding exchanges where credit cards are not needed like Unocoin(India) ?Or localbitcoins ? Just a suggestion.
thanks for that, this clarifies how bluetooth transaction works, is very old thread but still usefull, and this give me an idea from one guy that says if you disconected everything even chip, this maybe in theory could be a cold wallet.