If any such persons be desirous of purchasing such lands, then within six weeks after such offer of sale they shall signify their desire in that behalf to the promoters of the undertaking; or if they decline such offer, or if for six weeks they neglect to signify their desire to purchase such lands, the right of pre-emption of every such person so declining or neglecting in respect of the lands included in such offer shall cease; and a declaration in writing made before the sheriff by some person not interested in the matter in question, stating that such offer was made, and was refused, or not accepted within six weeks from the time of making the same, or that the person or all the persons entitled to the right of pre-emption were out of the country, or could not after diligent inquiry be found, or were not capable of entering into a contract for the purchase of such lands, shall in all courts be sufficient evidence of the facts therein stated.