[Mauzen]

pawn Код:

public OnPlayerSpawn(playerid)
{
        if(IsPlayerNPC(playerid))
        {
            new npc_name[24];
            GetPlayerName(playerid,npc_name,sizeof(npc_name));
            if(!strcmp(npc_name,"Cocaine1",false))
            {
                SetPlayerSkin(playerid, 144); // your skin choice for NPC
            }
            if(!strcmp(npc_name,"Cocaine2",false))
            {
                SetPlayerSkin(playerid, 144); // your skin choice for NPC
            }
            if(!strcmp(npc_name,"Cocaine3",false))
            {
                SetPlayerSkin(playerid, 144); // your skin choice for NPC
            }
        }
    return 1;
}

Just remove all the return 1, except the very last one.
And for the performance and a clean style dont do the
IsPlayerNPC, GetPlayerName stuff again and again. Checking it one time is enough, if you got the name, just check them one directly after the other.