About 95% of our domestic stuff is 4 weekly, the rest 8 weekly. The price is the same as it takes no longer to clean them; anyone who says differently is telling porkies 
Why are people telling porkies , add some birds 2 4 weekly clean easyier to come off add them same bird to same house for double the amount of time then you will have more mess which in turn will take longer to clean, that's just one reason, but look at it from a business angle
if you charge the same thats cool for you , I charge more but my price is not just for the clean it has everything included in it, as it does takes longer per customer and this is for the following reasons:
8 weekly you have to find 2 customers to fill one 4 weekly places, meaning twice the amount of billing, accounting, more fuel, more wear on van, more water and more time talking to customers.
hope this explains why i don't agree with you
