@Clay29 I always make sure to fulfill the 'respond to inquiry/request' within the specified amount of time (usually instantly).
I don't decline requests unless I have to; usually I get the guest to decline so it won't be counted against me.
I also don't see any reason to decline an inquiry, so I never do so. I just ignore the guest if needed (after fulfilling the quota/initial reply) which is basically as good as declining.
A neat trick that I sometimes use to get them to stop messaging me. I block off a day or two in their requested dates, and then I tell them that 'Sorry, the dates that you have requested are no longer available.' That basically always works.