That rug I posted closed a lot more, something in the mid twos - but that give you an idea of where the market is. The one on ebay is actually a live auction, which means that it's a legitimate auction house which also just happens to be posting the rug on ebay for online bidders should they be interested.
It would be tough to find something 10x8 or larger for around $400 antique in perfect condition. That's not to say it's impossible, but it's highly unlikely. I think I told krow before there was a customer of mine who came in and told us about a very large rug which was in a rental she had. The landlord asked her if she wanted the rug when she was leaving behind the lease. He gave it to her free of charge, she accepted after many years of liking it, then found out the rug was some valuable Indian carpet which sold at auction around $80,000 +. So I guess the point is you certainly can come across some serious bargains, but it has a lot to do with the right time and place as with anything else. To me, it seems like the Persian Rug market is taking a hard upswing with these old pieces.
Yes ebay can be a crapshoot, and more often than not, you're going to get burned. The problem is that even people on craigslist buy rugs on ebay to sell locally, just
look at UES on craigslist. Sifting through these can be tough, at least here in NY I would imagine. The other problem is people bring these rugs they've had for years to auctioneers, get an estimate, and then think they can sell it for the same price. I went to a yard sale just yesterday. There was a beautiful old Karabagh rug which was in fair condition. I looked at the price tag, then asked the owner what they knew about the piece. It was probably 3x4 or so, she knew nothing about it and the price tag said $2000!!!! I looked at them as though they were crazy. She said she had it appraised by an auctioneer. The problem here is 1, she had no evidence of such, 2, you cant ask the same price that an auctioneer would fetch if you're an individual. There's something prestigious about purchasing a rug which was published in a sotheby's auction cat. that you have that item printed and imaged on paper, and have the rug on your floor. Private party value, forget it! What people do is they hear what they want. They're told the rug is worth 1000 replacement value, $400 retail (for example) and try to sell the thing for $1000 when private party should be at least 30% less than retail! ridiculous - the point is, even craigslist is going to have its pitfalls, as I believe the case is with the kerman posted earlier.
As for what to look for with these rugs, I mean the first and most important thing with older rugs is condition. 1: Condition means everything. I have one rug I bought not too long ago that if it were in excellent to near mint condition, it would probably be worth $15,000 retail. However, in the present condition, it's probably worth no more than $600. After condition, I would have to say goodness of fit: does it meet your criteria. Rugs are meant to serve utility and art. If it does not meet your design and style needs, it does not serve it's purpose. Now, if you want a more straightforward answer than this, your best bet is to go with "timeless designs and colors" as Dave would say. Otherwise, there are certain Persian rugs the market seems to have forgotten. Silk heriz carpets for example almost always seem break estimates by a fair amount , however other notable classes of rugs seem somewhat depreciated.
What is most desirable and valuable? Honestly I would stay away from pictorial rugs, prayer rugs have never had a strong backing here, I would stay away from rugs that have been painted, dyed after production. I would stay away from brightly colored carpets, or rugs with dizzying patterns and other. Trust your instinct - if you think most people would consider the rug ugly yet you like it, the rug probably doesn't have the investment potential you're looking for. But hey, trends change...