If they were worried about it being treated as a gemach, all they needed to do was make a policy that they only take back items in new condition with the tags on.
The fact that there are more conditions than that indicates that they are trying to cut down on all returns, including wrong sizes, changes of mind, and the item not looking as expected.
I have mentioned before that I sell online for parnassah. While I never heard of this company before and do not have such polices. Unfortunatly DY your plan doesnt work
In a regular Bricks and Mortor store, when someone returns something and it looks used or the tags are removed, you just refuse the return , However online its much more difficult as you are in possesion of the item and the buyer could file a chargeback via paypal or his credit card and even deny the tags were removed and there isnt much you can do. At least the item is in your posssesion and you wont lose more.
Ive been there were an unauthorized return was made and after discussing it with other online sellers, They agreed it was better to keep the item and give the refund otherwise not only could you be out the item, you could be out the money and the credit card companies and paypal generally are pro-buyer, not pro-seller