Most people looking for used tanks only want the basics..tank,filter,heater,hood/lighting and stand. I know when I search around for tanks I dont have any interest in the deco in the tank and if there are fish in it already it will all depend on what they are compared to the price I am paying to make it worth the hassle to try and transport live fish from point A to point B. The going rate most people on the forums go by is $1 a gallon for used tanks and equipment .... then I figure in alittle extra for a stand. So for a used 55g with basic equipment and stand I wouldnt give much over $75 for it..... unless it had some high dollar filters,lighting ect....then I might adjust alittle according to that.