Certain does not help the OP's issue of dealing over the phone, as you never know who you are going to get, but in person it is helpful to cultivate a relationship with a live knowledgeable salesman.

For the longest time I purchased much of my equipment from Fairview Photo in Brantford, as I got to know the previous owner and his long-term experienced staff. Not in Brantford much these days, and the owner sold it, so...

Currently working with a salesperson knowledgeable in film and digital at Henrys, and find that a good relationship.

With the current emphasis on digital, young staff, and likely high turnover, little one can do other than try to make it as easy as possible and reduce the opportunity for them to get it wrong. Not ideal, but the alternate is to just complain...