gistfile1.cs

abstract class BaseViewModel : IValidatable { 
  public LocationViewModel Origin { get; set;}
  public LocationViewModel Dest { get; set; }

  override IEnumerable<ValidationResult> Validate( ValidationContext context ) {
    //copy ValidateFMViewModel logic
  }

  protected abstract LocationsCheckResult Check(string originToCheck, string destToCheck);


}

public class SearchCriteriaViewModel : BaseViewModel { ... }