I always use the flexible dates button when searching and look at one night stays first. Then I look at two night stays etc.
The site never seems to do an average price calculation ; charges the highest night price for a multiple night stay ( and sometimes if you are lucky - the lowest)
And sometimes charges what seems like an arbitrary higher price
fx. I was booking Hilton Strassbourg : first night 104 €, second night 104 € and third night 90 €; all three nights in one reservation = 139 € per night.
And standard rooms was available for all three nights.
Booked two reservations then and the hotel was clever/nice enough to recognise it as one booking and charged me for both reservations in one transaction (pre-paid booking).