Buy Hearing Aids from EBAY?

I see there are so many attractive prices to buy hearing aids online. If I do purchase them online? Can I go to any local audiologist to set up the hearing aids?

Is there any hearing aids centres where I could try out MicroPower IX, Savia Art, Sonic Innovation Balance, and Starkey Destiny? I noticed that each audiologist only carries one brand more than others. I noticed that hearingplanet seems to carry pretty much all of them. I guess I have to arrange a trip to The US. Most Audiologist in Singapore and Australia seem to carry one brand or another.

Thank you in advance!