The successful way to sell a tank.

Selling tanks clean and empty are always a good idea. Throw in all the extra stuff for like 20$ or whatever. It's best to sell the fish separate for personal reasons, as most people want to stock a tank their way. Your price could also be too high. Generally a dollar per gallon or two if there's a stand is a good way to go. If there's extras just tack on a little bit to the price, but not a whole lot. You're certainly not going to get what you payed for it.

It probably is more appealing to the buyer to sell them clean and empty, but it's hard to say why it's not selling without a copy of your write up. Most likely, it's the price, and the market. If lots of other people are selling similar systems then yours might just be getting lost in the midst of it.

I've never bought a tank with fish included (not sure if you are planning on including the fish or not) just because it's more trouble and pressure to have to set up the tank immediately when I get home and transport the fish. Best to sell/trade in the fish separately, if you're not keeping them.

Depending on the market, and not knowing what you have included for filtration, I would expect to pay about $75 or so for your standard 30 gallon set up, and maybe $150-200 for your 72 gallon, since it's a bowfront and has a deluxe light fixture.

Yeah, I'd say it's definitely the price. Oak tanks and stands aren't really as appealing as the more modern ones. The stand and light fixture are very standard, looks like. Even with a name brand canister filter, powerhead and heater I wouldn't expect to get more than $125, tops, and even that's a stretch since there are so many bargains out there. It's more trouble, but you might be able to get more if you sold the canister separately...as long as you estimate your shipping correctly.

Hmm, I would say definitely sell the discus separately. The majority of people don't want to keep discus, honestly. They have a reputation for being fussy and are kind of specialized. Sell them separately (no idea for how much) and then sell the tank. Even with all of your equipment (and you do have high quality equipment!) you would be very lucky to $300, at least in my neck of the woods. $500 for a freshwater tank is very big money in the used market. I see 75 gallon reef ready tanks going for that all the time.

Aquariums depreciate tremendously, unfortunately.

I sell alot of tanks on craigslist (buy low, use if need be and sell higher or sell old equipment). Really the only way to get "top dollar" for your used tank is to drain it, clean it,and list what it has. Best setup goes with tank, stand, top, lights, filter and anything after that is bonus. Since the fish are discus its probably in your favor to sell seperately since they are worth money and whoever gets the tank will almost deffinitely not be able to take care of them properly. Honestly the 30gal to sell is a bit high... just because of the gallon-age if its that black tank it is beautiful! But there are so many cheap tanks out there I just picked up a 75 gal with stand, glass top, canopy, filter, bubbler, 100lbs of gravel, fish and decor for $200...

Post it here and lets see what we can identify!