public class CarViewModel : ValidatableObject
{
    public CarViewModel()
    {
        Validator = GetValidator();
    }

    private IObjectValidator GetValidator()
    {
        var builder = new ValidationBuilder<CarViewModel>();

        builder.RuleFor(vm => vm.Make).NotEmpty();
        builder.RuleFor(vm => vm.Model).NotEmpty().WithMessage("Please specify a car model");
        builder.RuleFor(vm => vm.Mileage).GreaterThan(0).When(model => model.HasMileage);
        builder.RuleFor(vm => vm.Vin).Must(BeAValidVin).WithMessage("Please specify a valid VIN");
        builder.RuleFor(vm => vm.Description).Length(10, 100);

        return builder.Build(this);
    }

    private bool BeAValidVin(string vin)
    {
        // Custom vin validating logic goes here.
    }

    // Properties with realization INotifyPropertyChanged goes here.
}