AC

#define MAX_DISTANCIA 30.0
new bool:PlayerVendo[MAX_PLAYERS][MAX_PLAYERS];

public OnPlayerUpdate(playerid)
{
	foreach(new i:Player)
	{
		if(PlayerVendo[playerid][i]) return true;
		if(GetPlayerDistanceFromPlayer(playerid, i) <= MAX_DISTANCIA)
		{
			ShowPlayerNameTagForPlayer(playerid,i,true);
			PlayerVendo[playerid][i] = true;
		}
		else
		{
			ShowPlayerNameTagForPlayer(playerid,i,false);
			PlayerVendo[playerid][i] = false;
		}
	}
}
stock Float:GetPlayerDistanceFromPlayer(playerid, targetid)
{
        new     Float:fDist[3];
        GetPlayerPos(playerid, fDist[0], fDist[1], fDist[2]);
        return GetPlayerDistanceFromPoint(targetid, fDist[0], fDist[1], fDist[2]);
}