I agree with Sharafi, and Nick has a good point there about Bakhtiari. There's a really good book on the woven structures of single wefted carpets and how to distinguish the different areas. When I remember the title I will pass it on. Anyway, I now try to provide information on rugs as opposed to value - it takes a lot of consideration to figure value ranges.
It sounds like after joining the forum you may be buying for personal and perhaps collection maybe resale? The only recommendation I can make is to buy where you feel comfortable. If someone paid 1500 retail and they can show documents to support that, but they have enjoyed the rug in-home for the last 10 years and are trying to sell it in used condition with wear and in need of servicing, they need to be realistic about their pricing. For high end rugs, prices have maintained fairly well. However, for commercial and mediocre rugs, values in my opinion are quite depreciated.
Bottom line - not speaking to this rug, but carpets and purchasing in general - If the 1500 rug needs 250 in servicing and cleaning, it doesn't make sense for the rug to be priced at $1250. Also remember, the buyer has enjoyed the carpet for many years which means it's subject to wear and environmental factors. Often in cleaning, unseen cosmetic anomalies can also appear and the pile may show more recessed or the wear or true condition be more apparent. Colors may run, perhaps some white knots show through, or the rigors of washing a rug may loosen selvages or overcasting. Whoever buys the rug is assuming risk of investment. When purchasing a rug in need of a wash (and all rugs should be washed) there is yet another risk. The big question is - where do you feel comfortable making an investment? Is the purchase part of a business model, or are you a collector and are willing to pay close or at retail for the right piece?
As a last note, this rug does appear to have the character of some of the better in the type. Meaning, while not a collector piece, it appears to be an above average example for the type.