What a difference a complaint makes

Last summer we got someone round to paint our decking. It looked fabulous. Just like on the can. However, 5 months down the line its not looking so fab. Despite not actually walking that much on it or using it for entertaining it has now gone patchy in places.
Surprisingly I found the receipt for the stain and thus ensued a discussion with B+Q and Ronseal as to who to report this fault to. Back and forth emails on how we'd done the prep of the area, painting and aftercare was discussed. 
Although no liability was accepted as a gesture of goodwill we received a nice amount of paint/ stain to try again - result.
However, I don't think this time we can justify a man to do it this time and it'll fall to me to paint it this time.