It is highly unlikely that any transfer company will compensate for missed flights other than a refund of the fare (if you are lucky).
Not much comfort if they are responsible for you missing your flight, but many travel insurance policies will cover for missed flights when using public transport.
Few, if any, will cover if your journey was made by a private or rental car.
Always ensure that you have adequate travel insurance and for those who rent their properties, it is advisable for many reasons, to insist that your guests have insurance and provide you with details when they book.
The protection and peace of mind of having cover is worth the small cost. There are some really cheap deals out there, use a 'screenscraper' to find the best deal.