[Konstantinos]

pawn Код:

// global
new
    bool: In_Pickup[ MAX_PLAYERS ]
;

// OnPlayerConnect
In_Pickup[ playerid ] = false;

// Where you want it to stop showing all the time.
if( IsPlayerInRangeOfPoint( playerid, 1.0, X, Y, Z ) ) // CHANGE THE COORDINATES
{
    if( !In_Pickup[ playerid ] ) 
    {
        In_Pickup[ playerid ] = true;
        ShowPlayerDialog( ... );
    }
}
else 
{
    if( In_Pickup[ playerid ] ) In_Pickup[ playerid ] = false;
}