private bool SetMissingCarErrorIfNeeded(ref string errorMessage) {
var list = CarsOrTheirIds.Where(x => !x.CarExists).Select(x => x.CarId).ToList();
if (!list.Any()) return false;
errorMessage += (list.Count == 1
? string.Format(ToolsStrings.Online_Server_CarIsMissing, IdToBb(list[0]))
: string.Format(ToolsStrings.Online_Server_CarsAreMissing, list.Select(x => IdToBb(x)).JoinToString(@", "))) + Environment.NewLine;
return true;
}