C Can you fit our shower?
R Yes, but you need to tile the wall first.
C Okay, what sort of shower should we go for?
R Something that will accept surface pipework, how about xx? (It was a friend, so I thought I'd bother to give free advice in this instance even though I wasn't supplying the kit.)
Months later...
C How about this model?
R No, because it won't accept exposed pipework.
C How about this one?
R See above.
...
C What was the one you suggested?
R I had suggested xx.
C I've researched it and think they'd all work [i.e. even the ones I said weren't suitable even though I've checked the M.I.s] , but happy to go with your suggestion.
R Okay, but you do realize I'm probably not going to be able to fit it? [as I have massive commitments 250miles away].
C No, I didn't know that because I heard you would be around for several weeks [not sure where the person heard that from!] Oh well, thanks, you've been really unhelpful!
I just hope she ignores my 'unhelpful' advice and orders the wrong one and the other local plumber can't fit it.