I believe you are looking for
app/code/core/Mage/Shipping/Model/Carrier/Flatrate.php
Which looks like
public function collectRates(Mage_Shipping_Model_Rate_Request $request) { if (!$this->getConfigFlag('active')) { return false; } $freeBoxes = 0; if ($request->getAllItems()) { foreach ($request->getAllItems() as $item) { if ($item->getProduct()->isVirtual() || $item->getParentItem()) { continue; } if ($item->getHasChildren() && $item->isShipSeparately()) { foreach ($item->getChildren() as $child) { if ($child->getFreeShipping() && !$child->getProduct()->isVirtual()) { $freeBoxes += $item->getQty() * $child->getQty(); } } } elseif ($item->getFreeShipping()) { $freeBoxes += $item->getQty(); } } } $this->setFreeBoxes($freeBoxes); $result = Mage::getModel('shipping/rate_result'); if ($this->getConfigData('type') == 'O') { // per order $shippingPrice = $this->getConfigData('price'); } elseif ($this->getConfigData('type') == 'I') { // per item $shippingPrice = ($request->getPackageQty() * $this->getConfigData('price')) - ($this->getFreeBoxes() * $this->getConfigData('price')); } else { $shippingPrice = false; } $shippingPrice = $this->getFinalPriceWithHandlingFee($shippingPrice); if ($shippingPrice !== false) { $method = Mage::getModel('shipping/rate_result_method'); $method->setCarrier('flatrate'); $method->setCarrierTitle($this->getConfigData('title')); $method->setMethod('flatrate'); $method->setMethodTitle($this->getConfigData('name')); if ($request->getFreeShipping() === true || $request->getPackageQty() == $this->getFreeBoxes()) { $shippingPrice = '0.00'; } $method->setPrice($shippingPrice); $method->setCost($shippingPrice); $result->append($method); } return $result; }
If there is custom code involved in calculating the shipping rates, I would look for a module that is rewriting the collectRates method, there is also a couple other events they could have hooked into to re-calculate the shipping costs, I would also look at the config.xml files of any custom modules that have been written.
Hope this helps
