jecasc - 5:59 pm on Oct 22, 2012 (gmt 0)
You are so wrong it hurts. Bottom line - you should stick to your line of business - what ever it is you are doing and under no circumstances ever do ecommerce.
The whole website you are basing your statements refers only to shipments where no contract at all exists between the two parties involved. The sending of unsolicited goods.
The advice to contact the sender in case of an honest shipping mistake also refers to a case where your received goods without any contracts existing between you and the sender - for example if you receive goods because of an error on the shipping label. Or you receive an unexpected shipment but see from the invoice included that the shipment was not meant for you.
In the OPs case however there is an existing contract between the two parties involved which changes everything. The OP made a mistake while fulfilling the contract.
When the goods delivered do not conform to the sales agreement the buyer now has the right to reject the goods - not to keep them in addition. Which means informing the seller that the goods are not as described in the contract and give them back and then demand the fulfilling of the original contract.
Imagine what would happen if everytime a mistake was made during the fulfilment of a contract the buyer could keep everything. Oh you delivered the sofa in red instead of blue. Please send me the blue one and then I'll keep both for the price of one. Oh - the bike has the wrong saddle. Thanks for the free bike - please send me the correct bike I'll keep them both for the the price of one. The house you built for me is quite nice, but the porch is painted the wrong color. Thanks for the free house I'll keep it and you have to build me a new one in addition. Doesn't work that way.