I have used Skyscanner and Kayak to check flight - but never buy ticket, as they always redirect you to site that I am not familiar with, are these booking sites trustworthy??

Many thanks.

Skyscanner, Kayak and a number of competitors connect the customer to a wide variety of sites that sell tickets. Some of those sites are operated by airlines, some by on-line ticket agencies. Nobody can give you a blanket evaluation of how reliable all of them are.
Once the connection is made, Skyscanner et al have no more role in the ticket sale.
Some of the on-line agencies have been around long enough to grow into major companies. They do have the advantage of being able to combine airlines into a multi-flight itinerary.
Opinions on this forum and elsewhere tend to rate these agencies as okay for straightforward purchases but suggest it may be difficult to obtain help in case something goes wrong or you want to make changes. Again, some operations will probably be better than others in such circumstances.

Very well explained - really appreciated.
Thank you..

I use Skyscanner then check the airlines price. Some of the resellers may not be the best price.
I had a big drama with Bravofly for example, and Skyscanner helped me resolve the issue.

good to know - thanks