Basement waterproofing and a single source of materials supply, or is there a viable shortcut ?

When winning a tender for a project that a.n.other, such as a specialist manufacturer has delegated you for, (so no big cost to you per say), would you compromise that mutually beneficial relationship, or perhaps worse still, potentially jeopardise the clients guarantee by installing a mixture of components from various manufacturers, especially when they were already specified for you to price at, and the originator of a lead indeed had all of the appropriate products readily at your disposal ?

Well unfortunately this does happen, and indeed a colleague of mine had to only recently visit a main contractor on site who had rightful and serious reservations about the above issues, as he didn't feel he was getting what he was "supposed" to be paying for, and my colleague naturally and ethically had to make the appropriate comments regarding both the original deviation from the original specification, (and after-all, the installer wouldn't be able to employ my colleague should he get dismissed from his job by defending the installer) that not only had differing systems been utilised, such as slurry coatings which had been substituted, but also that there were different manufacturers brick plugs and tapes used over differing manufacturers cavity drained membranes, (yes, several makes of membrane in one basement !!) as well as the pumps not being of the same specification too, so given that the system had now become a Hybrid one, there was little he could do to offer any assurances to the client et al, especially in regard to product guarantees, compatibility / manufacturers liabilities etc..., (Big Oh Dear indeed I hear you say)

Now whether the installing contractor just happened to have a mixed bag of differing suppliers materials "knocking about in his lock up", or he may have thought he'd "saved a few quid" on sourcing the correct materials from the supplier who had not only delegated his company as a candidate for the contract, but who had also spent quite some time attending inception and multiple design meetings, at considerable cost of course, but I couldn't possibly comment on that aspect.....could I ?

but anyway, forgetting the manufacturers financial losses for the time being, here's the rub for the installer, the M/C is now seriously considering to withhold payment, and wants to now see all the test accreditation's for the products used, and assurances about compatibility etc, as they were not on the original specification which was tendered for, (Lab tests for differing products compatibility can be lengthy and expensive too of course) and he is now even considering to instruct the installer to remove the unspecified materials and replace with what was in the spec which he had tendered for before payment can be considered.

Anyhow, technicalities and ethics aside, I do have to wonder what that particular contractors attitude to associated risk and Price v Cost is now, or has he got himself a bigger lock up to store even more odds n sods for the next victim ?

And I suppose the moral of the post is, keep it straightforward, tender for what was asked, and deliver as proposed, and then guess what, you may even get that M.C.'s next project without the rigours and financial costs and time that the originator of your free lead went through too ?