Am I using the controller correctly or should this code be in the models?

Question

PHP

This code is in the controller, is this correct, or do I need to create a method in the models and pass values ​​there?

public  function  buyProduct($id){
        $product = Product::where('id',$id)->get();
        $userId = Auth::user()->id;
        $sellerUserId = $product->first()->seller_user_id;
        $sellerUserIdBalance = User::where('id',$sellerUserId)->get()->first()->balance;
        $productOwnerId = $product->first()->owner_user_id;
        $productPrice = $product->first()->price;
        $userBalance = User::where('id',$userId)->get()->first()->balance;

        if($userId == $productOwnerId){
            $response = [
                'response' => 'You cant buy your product'
            ];
            return response($response,201);

        }
        elseif ($product->first()->status_id == SOLD){
            $response = [
                'response' => 'This product is sold'
            ];
            return response($response,201);
        }
        elseif ($productPrice >= $userBalance ){
            $response = [
                'response' => 'Not enough money'
            ];
            return response($response,201);
        }
        else{
                Product::where('id', $id)->update(array('owner_user_id' => $userId));
                Product::where('id', $id)->update(array('buyer_user_id' => $userId));
                Product::where('id', $id)->update(array('status_id' => SOLD));
                User::where('id', $userId)->update(array('balance' => $userBalance-$productPrice));
                User::where('id', $sellerUserId)->update(array('balance' => $sellerUserIdBalance+$productPrice));
            }
            return  Product::where('id',$id)->get();
        }

Answer 1

public function buyProduct($id){
$product = Product::where('id',$id)->get();

Well, here, as it were, you can immediately receive a finished model object in the parameter.
But even if you get by id, isn't it better to use one of the find..() group methods?
Conclusion: Lark's knowledge is near-zero.
Move on

$userId = Auth::user()->id;
$sellerUserId = $product->first()->seller_user_id;
$sellerUserIdBalance = User::where('id',$sellerUserId)->get()->first()->balance;

That is, we first get the user , take his ID, then look for this user ID in the database (and we already got it earlier) and get it again to pull the balance from there.
Conclusion: Lark's knowledge is near-zero.

User::where('id', $sellerUserId)->update(array('balance' => $sellerUserIdBalance+$productPrice));

And here we once again turn to the user table. What for? We have already received a user a couple of times ...
-------------------
But in general, on the issue, it seems to me the norms.
It is in the controller that we determine whether this user can make a purchase.
Well, or as an option, you can throw it in the middleware. Provided that these checks can be performed in subroutes. If the check is only in this route, then the rules.