Many a times when you directly go and deal for water-sports they try to charge you 10x the actual cost.
In Bali, if you hire a bike, do think before paying for parking. It is being observed that local scammer pretend to be parking Vendor and get money from you.
In many parts of Bali, products are being sold for 20 times their actual price. For example the Dreamcatcher in Ubud is 15000 IDR in cost and for same thing they are asking 150000 IDR in Kuta.
In Bali, you might be scammed into paying for a SIM card that will never get activated until your stay there.
Beware of SPA centers in Bali that might force you to empty your pockets. SPA should always be done in an authentic place.