What expression would you use for a impressionable person (a decision maker like a boss or potential customer) who comes to your facility (office, shop, garage, showroom) makes you do all the leg work for an critical suggestion/advice, promises you of a deal and then just for a sake of second opinion goes with his chosen/favorite dealer having contradicting advice and placidly comes informing you of superseding deal blissfully oblivious of his misconduct.
I would say the person is "unreceptive", to the ideas or suggestions of others.
1. not tending to receive new ideas or suggestions favourably
Collins English Dictionary
Or, considering they originally sought ideas but rejected them anyway, I'd say they're "dismissive", of other suggestions.
Feeling or showing that something is unworthy of consideration.
Oxford Living Dictionaries