Hi Gavin, simply turn the problem around and look at the situation as if you were the one buying in the services. What would you want to know about your prospective supplier? Basically you need to make them comfortable dealing with you so why not start with a brief company history, who you have worked for, what you have done, some contact references, insurance details, any quality or envirnmental credentials you have (if you don't have the "badges" a statement saying you are working towards them is better than nothing) geographic areas you cover, job size capabilities etc
Don't worry about how flash it looks as they will be more interested in a couple of A4 sheets which are factual yet get across the point they can confidently pass over their 'chore' business to you as you personally are going to take all their cleaning worries and troubles away from them.