Converting Pound to Market?

[Abronsyth]

Hello!

So I would like to turn the pound into more of a user-to-user market. So, a user chooses to send their pet to the market. The pet then appears in the market (a modified version of the pound), and then when another user buys that pet, the original owner who sent the pet to the market is awarded with the payment that the pet is sold for (as determined by the admin).

Now, I am pretty sure I can figure out how to use a pet's rarity to determine how much the value is (if $rarity = common {$marketvalue = 100}, essentially), and how to subtract that amount from the purchaser's account, but I'm not sure how to then see to it that it is added to the seller's account?

If anyone has ideas, that'd be amazing! If I figure it out before then, then I will be sure to share it with everyone as a mod :)

-Abronsyth

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Edit:
Check here for the latest chunk of code!

[NobodysHero]

Oooooo. This would be awesome! Yes, please!

[Abronsyth]

OK, so far I have managed to get it to determine cost based on rarity, and subtract that amount when the user buys the pet. I can also make it add that rarity-based-amount as soon as the seller chooses to send the pet away. However, I am having issues with getting it to add that amount to the seller's account once someone else buys the pet. Here's my code so far;
pound.php adopt function

PHP Code:

            if($this->settings->cost->active == "yes"){
                $adopt = new OwnedAdoptable($pound->aid);
                        if($adopt->getRarity() == "Common"){$sellvalue = 50;}
                        elseif($adopt->getRarity() == "Uncommon"){$sellvalue = 75;}
                        elseif($adopt->getRarity() == "Rare"){$sellvalue = 100;}                
                $cost = $this->getCost($adopt);
                $mysidia->user->changecash(-$sellvalue);
                $seller = $mysidia->db->select("pounds", array("lastowner"), "aid ='{$adopt->aid}'")->fetchObject();
                $sellermoney = $mysidia->db->select("users", array("money"), "username='{$seller}'")->fetchObject();
                $profit = $sellermoney + $sellvalue;
                $mysidia->db->update("users", array("money" => $profit), "username='{$seller}'");
                $this->setField("cost", new Integer($cost));
            } 


If anyone notices some major flaws I'd really appreciate it if you could share :) I'm running into this error:
Catchable fatal error: Object of class stdClass could not be converted to string in /home/inekelmy/public_html/pound.php on line 85
This is line 85:

PHP Code:

$sellermoney = $mysidia->db->select("users", array("money"), "username='{$seller}'")->fetchObject(); 


It's subtracting money from the buyer, and adding the pet to their account, but the seller is not getting money from it.