(2) The real market value of timeshare property, other than the recreational facilities, shall be determined by taking the value of each individual living unit as if such living unit were owned by a single taxpayer, without having been timeshared, and adjusting such value by an amount necessary to reflect any increase or decrease in such value attributable to the fact that such timeshare property is marketed in increments of time. There shall be a rebuttable presumption that the value of such timeshare property is increased by 20 percent of its value under single ownership by virtue of being marketed in increments of time. If the managing entity or assessor contends that the adjustment due to such ability to market in increments of time is less than or greater than an increase of 20 percent of the single ownership value, then the burden of establishing such adjustment shall be upon the party so contending. [1987 c.424 §3; 1991 c.459 §338]