It can be. It depends if the dealer is ok with an exclusive. They get "rewarded" for excluding the competition.
Even at 70% its a raw deal for the consumer. Hence, the rise of direct to customer cable companies.
With som much margin to play with, why isn't there a thriving grey market for cables selling new at 50% discount.
Some dealers will be happy to supply a middleman and take 20%-30%. It happens with other components plenty. I bought brand new JL113 subs for 50% of MSRP this way.