[Abernethy]

You didn't return false. (or 0. either way works).

pawn Code:

public OnPlayerCommandText(playerid, cmdtext[])
{
    if (strcmp("/help", cmdtext, true, 5) == 0)
    {
    SendClientMessage(playerid, YELLOW, "It is very simple,");
    SendClientMessage(playerid, YELLOW, "The more you kill, the more money you earn to buy weapons.");
    SendClientMessage(playerid, YELLOW, "Use /buygun to buy a weapon.");
    return true;
    }
    if (strcmp("/buygun", cmdtext, true) == 0)
    {
    SendClientMessage(playerid, YELLOW, "Use - /buygun [weaponname]");
    SendClientMessage(playerid, YELLOW, "baseballbat - $50 | sdpistol - $200 | deagle - $500 | mp5 - $600");
    SendClientMessage(playerid, YELLOW, "ak47 - $1250 | m4 - $1500 | Sniper Rifle - $2000");
    return true;
    }
    return false;
}