Webuycars Bad Service

I advertised a car to webuycars, they made a contact to view and buy the car. After they viewed the car they made an offer of R170K, Since I bought the vehicle from the auction they requested ownership and tax invoice where I bought the vehicle. That's when i suspected foul play in the process. After they received ownership and tax invoice documents they didnt wanna offer the agreed amount. They offered R120K which was R50K less what they offered in the beginning. Their service is very poor and manipulative.