Liens — Assessment — Foreclosure — Judicial sale — Vacation — Trial court abused its discretion in vacating and setting aside judicial sale where movant, who purchased property at sale, failed to make proper showing as to why equity demanded that sale be vacated and failed to establish that he exercised due diligence prior to placing bid on property — Purchaser’s mistaken belief that mortgagee’s interest in property had been fully extinguished not adequate cause to set aside judicial sale