Whether the spread is the "right" spread as you call it doesn't have anything to do with what is the "fair" or "right" spread. The "right" spread has to do with the efficient market hypothesis. If you believe that markets are efficient then you believe that the right price is the last current market price. If you do not believe markets are perfectly efficient (which most people do not) then prices will not be the "right" prices, but will correct eventually as people take advantage of the arbitrage opportunity.
Intersango only offers a discount on commission to to market markers but that is still a penalty, market makers should be rewarded, and make money for each trade.
hellobitcoin says they employ the make-or-take model, but in red words below their claim to use the make-or-take model, they state that they actually charge market makers 0.15% which is not the make-or-take model.
Several exchanges offer a make-take price differential. Intersango,
bitfloor and hellobitcoin come to mind.
I feel that the differential they choose is somewhat
arbitrary.
I have always felt that the make-take commission differential should
be no greater than the exchange's least count divided by the price of
btcusd. And, all exchanges violate this condition.
Why do I belive in this condition? For if this condition is not
met, then as a trader, it sometimes is cheaper for you to bid at
6.51 than it is to bid at 6.50.
Equivalently, here's, I believe, the problem from the exchange's
perspective if you violate this condition. The make-take difference may help you achieve a tight
spread and thus, a good price-discovery, but
both are illusory. For,
imagine that the true bid-ask frontiers should lie at
6.51-6.52. Imagine that your exchange is currently locked in at
6.50-6.51. Your exchange has seemingly discovered a price with a tight
spread. Is this the correct price? Even if traders are convinced that
the correct frontier should be 6.51-6.52, there is a *negative*
incentive for a trader to try to correct that imbalance.
