A key question is in order:
Do you have IB turned on or off. By saying you 'turned down a reservation', it insinuates you are on Instant Booking. If so, perhaps best not to be, considering you have a strict requirement that you would like to enforce, and tough to do so when you are bypassing the 'inquiry' step. Considering most do not even read thoroughly a listing's description, being on IB and expecting them to 'get the flic' is chancy.
If you do not have IB on, then it means this was no more than an Inquiry, which I doubt it would lower your 'Acceptance' %, since that rate only pertains to rejected or non-rejected Requests.