Question: Fraud Seller Prediction

I am checking a solution to prevent "fraudster" to create "store/ecommerces" to sell products as a fraud only.

Example:
Product: Stove brand Consul
Price: 100
Real price at normal shoppings: 500

Product: Washing machine Eletroclux
Price: 119
Real price at normal shoppings: 900

I am new in Machine Learning, so I would like a suggestion.