Its a good idea, but dont underestimate the time it takes to do it all, and the income you would generate whilst doing it offset against the cost of products etc. Start small though so its worth asking one or two local garages and starting from there, as you dont want to overload yourself, and end up dissappointing others that may take you on. If you enjoy it though, its worth a shot even if its just part time over the w.ends etc. 
this summarised what i was thinking really. i do enjoy it but who knows if the enjoyment will remain if i do it for an extra source of income?
i have a good collection of products already, so it will just be a case of replacing them as and when with the best combo of value for money and quality.
i have based my prices on the cost of traveling to the client locally within the £10.00, then for instance i could polish a full car in 30-40 mins easy, the same for wax and based this on an hourly rate of £6-7 for everything else, if that makes sense? but i guess this doent account for product used? maybe £7/8 for polish and wax layers would be better for me?
I can totally appreciate why you are doing this as you seem to enjoy it... but be warned about the enjoyment waning once you start doing it when you don't want to eg, inclement weather, extra hot weather, when you have a headache, when people are on a timescale etc?
garages tend to want the earth for a job that is done on a budget, they will also want it done quickly and tend to have rubbish payment terms
yes you can polish a car in 30-40mins easy... but what about the prep... loading your car up with gear, getting there, informing the client about your process, setting your kit up, finding water and power at the premises, filling buckets, getting pressure washer working, pre-wash, wash, wheels, rinse, clay, rinse, dry and then you are on to the polish?
if you are machine polishing cars you WILL need insurance that covers this, together with public liability insurance
if you are driving to and from a clients you WILL need to change your insurance terms
if you are using a karcher for non-domestic purposes then expect it to give up within a matter of months
buying in bulk will save you money in the long run, even though the outlay is more expensive, you will soon find that the cost of replacing your 'insert premium funky named product here' will become unviable as it is too expensive and you go through it like wildfire... so using autosmart/bulk valeting products is the only method.
so not only do you need to cover yourself for your time, but also for your business costs and materials
you'll find it hard to break through search engine rankings with that company name:
see here 