As far as warranty goes with most stores, online and brick and mortar, both only give 30 days in store.
After that you are generally the manufacturer's problem.
Furthermore with every RMA return I've ever made on an online purchase, the vendor ate the return shipping.
Ultimately it's no skin off of my nose to hang on to the box and shipping materials for the first month just in case of infant mortality.
However, I can honestly state that out of literally dozens of online purchases of music gear over the years I've had to deal with returns less than 3 or 4 times.
Quality controls on these things are pretty strict and it's not like a guitar where you won't know if it makes your fingers bleed until you play it.
Online reviews are usually pretty detailed and forums like ours allow you to ask other owners of the same gear the nitty gritty questions.
I mean honestly, if you are buying a Yamaha Motif brand new in a store, do you think a salesman will allow you two or three hours to run it thru its paces?
Keyboards are such complicated pieces of machinery you pretty much have to narrow down your options online long before you even consider pulling the trigger and dropping a few thou on a board.
My Kurzweil had such a heavy keyboard action when I first bought it, as it was my first hammer action board, that if I'd tried it in store I would have probably never bought it. But eventually it grew on me and I adjusted the velocity and now all my other synth style keys feel all cheap and loosey goosey and the Kurz is the only controller I now use.
Brick and Mortar stores may be a necessary evil for stringed instruments, but electronic keyboards are meant for e-commerce
Gary