new
    towtruck
;

towtruck = AddStaticVehicle( ... ); /* gamemodeinit / filterscriptinit */


public OnPlayerStateChange( playerid, newstate, oldstate )
{
    if ( newstate == PLAYER_STATE_DRIVER )
    {
        if ( GetPlayerVehicleID( playerid ) == towtruck && GetPlayerSkin( playerid ) != 23 )
        { /* if player is in the towtruck and his skin is NOT equal to 23 */
            RemovePlayerFromVehicle( playerid );
            SendClientMessage( playerid, -1, #You dont have towtruck skin );
        }
    }
    return ( 1 );
}