Yikes! I wouldn't do it! Storing all of it in the house would be out of the question, taking up too much space. Just carrying it into storage would require many person-hours of work. What if it smells? Would take a *ton* of time to sell that much on eBay or other places -- as someone else mentioned, a full-time job.
If you want to go ahead with it, definitely take a physical look at the fabric (and sniff it) so you know what you are getting. I would also find at least two other people to split it with you (one truck each? still yikes!). Make sure you have a place to store it. Arrange for people to help you move all that fabric into storage. Oh, yeah, and find out why he is selling it to make sure it is not stolen (although who would steal that much fabric?).