[Scenario]

Try this:

pawn Код:

dcmd_load(playerid,params[])
{   
    new
        // I removed your string and chk variables; you don't even use them here!
        iVehID = GetPlayerVehicleID(playerid), // added a variable to serve as the player's vehicle ID; this way you don't have to call the function 3 times
        rand,
        mrand;

    // I declared rand and mrand since there's no sense in defining them locally if you're going to need to define them in two places
        
    if(!strlen(params)) // you didn't need to use sscanf if you're only dealing with a single string
        return SendClientMessage(playerid, COLOR_ERROR, "usage: /load legal/ilegal");
    if(strcmp(params, "legal") || strcmp(params, "ilegal")) // no reason to use == 1, it's redundant
        return SendClientMessage(playerid,COLOR_ERROR,"usage: /load legal/ilegal");
    
    switch(GetVehicleModel(iVehID)) // use a switch statement, it's faster and far better looking
    {
        case 403, 514, 515: // if the vehicle's model is either 403, 514, or 515, do the code below:
        {
            if(!strcmp(params, "legal"))
            {
                Crcp[playerid] = 2;
                HasTruckLoaded[playerid]=1;
                rand = random(sizeof(RandomTruckPoint));
                SetPlayerRaceCheckpoint( playerid, 2,RandomTruckPoint[rand][0],RandomTruckPoint[rand][1],RandomTruckPoint[rand][2], 0, 0, 0 ,2 );
                            
                mrand = 50000 + random(500);
            }              
            else if(!strcmp(params, "ilegal"))
            {
                Crcp[playerid] = 2;
                HasTruckLoaded[playerid]=1;
                
                rand = random(sizeof(RandomTruckPoint));
                SetPlayerRaceCheckpoint( playerid, 2,RandomTruckPoint[rand][0],RandomTruckPoint[rand][1],RandomTruckPoint[rand][2], 0, 0, 0 ,2 );
                mrand = 100000 + random(1000);
            }
        }
        default: return 1; // if it's not one of those model ID's, end the processing on the command. "default" is basically "else" in an if-else control structure
    }
    return 1;
}

Read the comments!

EDIT: Sorry, missed a few things and adjusted accordingly.