Never had a problem with Adorama as far as retail purchases. I have only had to send one defective item back and they emailed me a prepaid shipping label. Part of the op problem may have been that Adorama may not felt the issue was due to a product defect. In that regard I would not expect any merchant to pay for shipping on an item I simply did not like - unless that is an advertised policy of course. As for any restocking fees, or shipping charges/deductions, you can almost always talk them into waving those if you are going to purchase something else.
I stated above I have 'never' had any problems with Adorama, but I must clarify that in regard to their used items, or items you are selling to them. On their used items it is not that they are 'unfair' in the implied sense, but you do not get all the same amenities you do with new products. To many that may be acceptable, but I think there should be no difference. I have purchased used items from many other merchants where after the sale support and service was no different at all.
If you are selling them something though you need to exercise a little caution. When the representative contacts you to discuss the estimated 'value' of the item, you have to dig unnecessarily to get them to give you the actual amount they will calculate their offer to you. For example you send them an item that they are currently selling (used) for $1000, they receive the item and contact you to let you know the item you sent them has a value of $700. That sounds great because you calculate in your head that they apparently mark up around 35% or so, and most of the people I have spoken with have gotten the same impression they are being offered $700 for an item Adorama sells used for $1000 (in the same condition of course). HOWEVER, what the representative is telling you is that they 'project' the value of the item you sent will be worth $700 in the next 30-60 days (even though they are still selling ones they have for $1000) so after they check out your item you are contacted with their offer that is 60-70% of the $700, NOT of their current selling price of $1000. Now I am not saying that the whole process is calculated on Adorama's part, but it does take more effort than it should to get them to explain that in advance.
The only reason I even mentioned anything about selling them your old equipment is because I experienced it first hand with a "like new" D300s, and was explained how Adorama offers the highest dollar on used equipment, the dropping value, etc, etc.. Then Adorama turns around and lists my camera online at even more than the one they had online before I sent them mine. (Had a friend call them with a story of internal issues that could be identified through the serial number series so they would give him the serial number of the camera listed online.) Practices like that just do not sit well with me...
I will not attempt to sell Adorama anything of real value as a result, but I have no issues dealing with them on any retail items and shop there all the time.