I think you should accompany with the plumber to buy the goods. You should buy only those things, which are easy on your pocket and of your choice. Take the plumber only to take advice.
(This one is gonna run and run...) The poster of this thread may well be a fully-informed individual who is perfectly capable of selecting the items he wants, and has examined all the alternatives. But I'd suggest that most customers don't really know the differences between 'ok' quality and a much superior alternative. They might not know that a superior alternative even exists. Every decent fitter will be able to rattle off a list of bathrooms manufacturers and put them in order of price and quality. So, if a customer comes to them with a list of their requirements, wouldn't it be professional for the fitter to sit them down and go through this with them; "These items are ok, but for the same price you can have this which is better quality, or this which costs a bit more but is far superior, or this which is the same but cheaper... etc"? Many customers can't see past B&Q or Wickes or Victoria Plumb... And even with that short list they are simply not in the position to compare these items for quality. Part of a good fitter's remit should be to guide the customer towards the best possible choice. And the fitter should then be given the task of sprucing them - they've earned it, and the onus of a fully-functioning install is on their shoulders too.
and oh yea, i almost forgot, if the plumber is buying the suites it won't take long to get in the VAT threshold, and that open a can of worms nobody need,
when quoting my bathroom fits I all ways give customer 2 quotes trade price and retail price then give them 2 options I supply or that them get the stuff giving them a list of companies I use find this way is best as it shows you are been honest
Many a times seeing many options at a same time makes me confuse, so I prefer looking at only 1 or 2 options.