Owners of an unlicensed pondside campground that has been banned from operating have signed a purchase-and-sale agreement with a developer, but have offered the town the right of first refusal in the estimated $2.4 million sale. Barbara and Ralph Holton, proprietors of Tispaquin Family Campground, put the 40-acre property up for sale in May after a decades-long battle over capacity. According to papers filed with the town, the couple has signed an agreement with Malloch Construction Co., which intends to develop the land for housing. In a memo to selectmen, planning director Ruth McCawley Geoffroy said the deal doesn’t seem to represent a “bona fide” offer because it depends on zoning changes. It also doesn’t appear to be certified, she said. If there is interest in purchasing the land, however, an appraisal would be the first step, she said.