Vibrams five fingers can be had for 1/4 to 1/5th the MSRP on eBay. Does anyone have experience buying them from there? How will i know if I'm getting an authentic shoe, sizing correct etc? I don't want to get some super stiff fake that leaves me with an injury or throws my natural form off kilter.
You won't, so be careful. Ebay is under no obligation to ensure the products you buy are authentic. These are likely "Grey narket" shoes that are authentic, but sold in such a way to avoid taxes/imported from areas where tax laws are different.
That said, I was recently gifted a pair of high quality "open box" headphones from the 'bay. The box was smashed up, product intact. They didn't have the $$$ cable that comes with them, so I bought one on Amazon and they sound fantastic. I threw away the instructions, but they were probably in a language other than English. YMMV. You can always confirm by contacting the manufacturer, but they will likely steer you away as a means to keep their "expensive, but worth it" image intact.