1st, how big is this sect that it can not only affect the market but the entire infastructure?
I will assume you are right in that the sect is indeed affecting the market. Now, substitute the sect with ABC Corporation that is hiring 1,000 employees. You would have no problem talking about how the corporation is having a positive affect on the market, right? "Ah, but it is only members of the sect that are paying the higher prices." That would be the same thing with employees of the new corporation, right?
The bias scare (my opinion) has appraisers paranoid about mentioning anything that has to do with "special groups". The truth is, the "bias police" (again, my words) is focused on appraisers providing their opinions that are not supported by hard data; that is their definition of bias.
You can't just not mention what is happening. Not only is it poor appraising but it is in fact a form of bias. My take would be to first, not say, "sect". Instead, say something like "private group". Then provide as much hard data that you can, i.e., number of sales, specific price trends, days on market, etc.; everything that you can so that your conclusions are an undeniable statement of fact and not an unsupported opinion.