I'am not supporting Credit cards to be honest and I love bitcoin however CC is reversible indeed but ... there is no double spend like on BTC if it doesn't get verified .
Of course there is. I spend $10 with my credit card in McDonalds. Then I chargeback, thus the payment gets reversed. Or in a way you could say it gets 'unverified' (in fact, a CC payment doesn't even get verified until 6-12 months). Then I spend the same $10 on a pizza. See, I just double spent my $10.
and imagine if the transaction don't get verified at all for a reason or another , it will end up going back to the buyer which will make the seller losing money .
1. It will make the seller losing money just as much as with credit cards or paypal. In fact, with credit cards or paypal it's even worse, because the seller not only loses his money, but also has to pay chargeback or refund fees (enforced by visa/mastercard/paypal, nothing you can do about it).
2. "Imagine if the transaction doesn't get verified", do you have any idea how extremely, immensely, extraordinarily unlikely this is?
It just doesn't happen. Especially not without using ridiculous trickery that is very easy to detect (like zero fee, or duplicate conflicting transactions, or tons of dust outputs, etc).
Seriously, try it. You simply won't be able to send a normal transaction and prevent it from being verified.