How do I avoid time-wasters and check a buyer is actually serious?

Qualify buyers before viewings: ask cash buyers for proof of funds (recent bank statements) and mortgage buyers for a pre-approval letter. Lock commitment with the Form F MOU and a ~10% deposit cheque so backing out carries a cost. A good agent pre-screens enquiries. Be wary of anyone pushing to skip DLD steps, trustee escrow, or independent title verification.