// We're getting the rows from the firstList that are not included in the secondList
var firstList = GetDoctorHonorariums(check.Value.DoctorID);

var secondList = form.gridControlServices.GetDataSource<HonorariumBM>().Select(x => x.service_or_cp_name).ToList();

var differences = firstList.Where(p => !secondList.Any(l => p.service_or_cp_name == l)).ToList();