While I don't subscribe to the tone of the OP, I agree that multiple - and bulk- bookings result in ruining it for everybody.
Unfortunately there is little to be done to counteract this 'free rider dilemma'-
look at it from the perspective of someone who books multiple times ( not talking about someone who places 50 different bookings - that is just plain silly)- when they weigh the benefits to be gained by them (more nights, options) by going against the collective interests of the group (that the bookings be honored) the latter often wins.
This is supposed to be a close knit community of people that enjoy travel and are trying to make the most of the experience
Therein lies the rub- you can’t assume an open forum to be a closed community - any one can link to the deal (or just copy it)
but what to do? if you’re the person who found the deal- should you not post it? then you decrease your leverage against the hotel (because its just you, not a group of consumers, against them) plus you want to benefit when others post deals.
and from the forums perspective? closing it off (which I disagree with in general) is only viable if you have a monopoly on the information- clearly not the case here- in fact because the mistakes are random- you want as many people in the pool as you can looking for them.
The only thing to do to partly alleviate the issue is stick a thread which explains why multiple bookings are detrimental for you in the long run.