What does your gut tell you?
My gut tells me that failing to do something as simple as posting proof of chip purchase despite numerous requests to do so, is a huge red flag, so I'm out.
My gut tells me that if these guys were scammers, they wouldn't be accepting Paypal unless they plan on fleeing the country immediately. It would be very easy for law enforcement to catch up with them.
Having said that, just because folks are committed to doing something doesn't mean they can actually pull it off. What could go wrong? Avalon could deliver the chips late or not at all. BKKCoins board design might not work.
Make no mistake about it, this is a risky purchase.