I recently booked a trip to London through kayak.com. The fares were in line with other sites and about $100 cheaper than American airlines. When I purchased the ticket through KAYAK, it sent me an email from another service, airfares.com, that said in addition to the ticket not being fully refundable, there was a $350 change fee and a $450 cancellation fee if the ticket was canceled or changed before the date of travel. Unfortunately I was unable to use the ticket so I contacted British airways to cancel. British airways told me that they could not cancel my ticket because it had been issued through an agent who they identified as International Travel Consolidators. British Airways could not provide me a working telephone number for their agent (International travel consolidators), I later remembered the airfare.com email and called their offices. This all occurred before the departure date and time. Airfare.com told me that there would be a $450 cancellation fee which would net about $110 refund, but to get that, I would need to pay them the $450 cancellation fee then wait 3 to 6 weeks to receive back the $450+$110 refund. If I can't even get a portion of your original payment back, I certainly wouldn't send them more money.
Kayaks position is that they are only a search site, not the ticket agent, so they have no responsibility or control. Based on airfare.com's change & cancellation policy requiring that you pay their fee on top of what you have already paid (which I believe is a scam), I would say NOT TO USE THEM, go directly to the airline or someone like Expedia, a travel agent or someone reputable who you can contact for service issues.