yep that's true I've got jobs with lead stains, I tell the customer about them before I commit to  take them on  I wont even bother faffing about trying to remove them, as I see it your there to remove dirt, bird shyte  not do a full overhaul your making a rod for your own back. the more you do the more they expect the longer it takes less time for other jobs to complete  you don't get better thought of.