Should I buy this vehicle?

You're best option is to take it to a local mechanic that you trust and have them evaluate the vehicle. Anytime you have a check engine or other idiot light on it's cause for concern. It might be a simple fix or it might be a major fix. For a SLIP light it might be one of the sensors. Low mileage, well maintained vehicles are always a good buy providing the price is right. If this has high mileage or signs of poor maintenance your better off staying away from it.