That's a naive, but not entirely unfounded concern. It's been quite common in the last few days to see enormous trading walls at certain values. If a large percent of the volume is set at an obscene price (200-1000% of the current average) then after a certain point, you effectively can't buy Bitcoin any more. There have already been enormous spreads (50$ difference and beyond) on several exchanges. That is not a sign of a healthy market to invest in.