Before agreeing to act as an agent for someone, you should check any legal requirements in the area where you are located. In some states, while it is perfectly legal to sell items that you own at auction, to sell those of someone else requires an auctioneer and/or auction business license or both.
Another thing I would highly recommend is to have a written agreement spelling out all the details of your business arrangement with the owner of the goods. Include details as to how you are to be compensated, who is responsible for fees, returns and refunds and every other possible contingency. Remember Murphy's Law states that whatever can go wrong, will.
Make sure to include a clause that details and lists what items are to be sold and what is to be done if an item is damaged and/or the owner changes his mind about selling it. I recommend that all items be turned over to you and that you inspect them thoroughly before accepting them for listing. Remember that the safety and security of the items is your responsibility while they are in your custody.
Personally, I would recommend having your attorney draft a standard agreement for use in these cases. Having things in writing will go far in settling things should things go south. (Remember Murphy's Law)
Of course, when dealing with relatives, it can get a bit tricky and you should remember that if things go awry, family relations are not easily mended. Be careful if you value family harmony.
"It is an intelligent man that is aware of his own ignorance."
