Yip, I would have to agree. On ebay you would get to keep the money yourself and would probably get more out of the 501. If the retailer buys it he will only buy it for cheap enough to where he can make a profit on it by turning around and selling it to someone else. Dont forget, when doing business on the internet, there is a loss on the shipping as well.
If you are not getting much out of a receiver (such as $25) and then had to pay shipping, you might as well keep it for that, especially a 301. I would buy 301's all day long if I knew I could get them for $25 if I knew they had no balance on them, was in working condition and was transferrable to me because I know of customers that would like to upgrade or need a receiver if their's go bad or need a cheap additional receiver.