Yep. I've been in that situation many times, having to explain why I'm quoting XXX for only 4 speakers when this other guy is quoting half the price for 12 speakers! I already have my canned "Not all speakers are created equally" and "Sometimes less is more" speech ready to go for clients like that... And for what it's worth I generally quote for the service, not on a per-speaker rate, but some clients like to see a system spec'd out on quote (which of course opens the door for non-apples to apples comparisons between vendors).
Well,
I've been on the organizer side many times, and sometimes (new) bidders don't specify what they will bring for a certain (fairly low) amount. They will i.e. quote something like "nexo array with subs", which tells me nothing. I want to know what and how many they bring, so i can check if the service requirements are met. I agree with you that after a while one should be able to trust the production company. Ofcourse there are many other deciding factors.
Usually the quotes you get over here is quite well specified, with coverage and stage plots etc.