And in I wade to retailers side of the net.
If they are not going to get asked questions about projects, maybe all tile shops should just be cash and carry then. Don't need experienced sales staff to offer recommendations. Just a Muppet who knows nothing keeping his eye on the self service checkout will be fine....... Reality check? Will the technical department you phone come and physically look every single job before they advise what you need? Do you really get every conversation in writing? And do you have that little confidence in what you are doing that you actually need it in writing?
Yes 99 times out of 100, the retailer can only go by the information they are given but that is the same as any technical department at the end of a phone line so there is no difference is there? But they both ask the right questions to paint the best possible picture and advise accordingly. If the client/tiler doesn't know the answer, send them off to find out.
If Lee hadn't seen the job but was told everything in great detail as to the substrate, prep and subsequent cracks appearing, would the advise he gives be any different? Probably not, but it doesn't automatically mean he's wrong. You should give most (won't say "all" cuz we know it's bollux) retailers some credit for knowing what they are talking about. Where do you think their training comes from? Couldn't possibly be from the very same technical departments you are quick to jump to for the answer...... or could it?