And a 6 month listing in this market is nuts.
I am a Realtor in Central Florida. May I ask why you think a 6 month listing is "nuts"? It's not that nuts in our market here. I certainly would not insist on a $1500 marketing fee (that seems a bit high and I am with RE/MAX so I know high fees, lol) but I would want to know, as a Realtor, that the seller is going to be realistic about how long it will take to market the property. It's very easy for your Realtor to let you know the average DOM (days on market) for a listing in your area. If this is close to 4 months, then a 6 month listing is ok. You should really understand how much your Realtor will outlay before they ever see a cent of commission. We don't work for free, just like you! If your home was on the market for 6 months and did not sell, it was priced too high. Simple fact. Price trumps everything and everything will sell for a price. Period.
If the OP is VERY REALISTIC about pricing and is listening to the recommended amount the Realtor is saying to list the house for (taking into account comps, short sales, bank-owned properties, days on market, etc.) then I would ask to see his/her marketing plan. (This is what you should have been shown before you ever listed with the Realtor in the first place.)
It does cost money to market a property. As a Realtor, I would also be wary to take a listing that had already been on the market 6 months. That's a stale listing and is much more difficult to market, especially if there has been no price change to warrant people taking a second look.
Best wishes with your sale! I know many of our listings do not last more than a month because we have a lot of investor-driven sales, but when we get a difficult seller or sometimes a difficult bank in a short-sale they do take awhile.
Tracy