[AndreT]

One small thing that bothers me, what's the model variable actually for or how is it assigned?

Also, a small thing to make your code better would be using a switch statement there.

pawn Код:

switch(model)
{
    case 534:
    {
    }
    case 533:
    {
    }
    //...
}

Something to make your code better structured (for some eyes that is):

pawn Код:

// instead of this:
if(response)
{
    switch(model)
    {
        // ...
    }
}

// act like this:
if(!response)
    return true;

switch(model)
{
    // ...
}

There's some useless returning as well...

pawn Код:

if(PlayerData[playerid][pcar] == -1) 
{ 
    SendClientMessage(playerid, COLOR_GREEN, "You buy REMINGTON=1"); 
} 
else 
{ 
    SendClientMessage(playerid, COLOR_GREEN, "You buy REMINGTON=2");
    return 1; // <-- useless return,
} 
return 1; // <-- this one will do the job