About 50% of the houses that I have cleaned on a 'custom built' round have been underpriced.
Wether that is due to undercutting to get the customer onto the books, or just inaccurate costing remains to be seen, but a lot of the customers have mentioned how cheap the work is compared to others, which suggests an undercutting approach rather than finding the properties that are in need of a wc.
Example: (Surrey stockbroker belt) 4 bed detatched house with original leaded (pannelled) glazing, plus conservatory, plus gge extension window, external clean: quoted £12!
Bt the way, remember that with a 'custom built' round you dont get to see the extent of the work at hand until your first visit, as it isnt you who has quoted.
I am having to honour initial quotes to maintain the new round, but its like trying to get blood out of a stone in upping the prices, and will remain so.
So beware.