Good condition means no rust on the bottom or one that has been properly cleaned and sealed. If one is good then it can be installed and used as is less paint work.
Excellent condition would one that is like new and they would be rare in this day and age.
Good restorable condition is one that still has fair thickness of metal skin left even though corroded. It would be one that is a candidate for proper cleaning and sealing before use.
The more work that has to be done, the less the worth of the assembly. Most tanks are rusted to some extent and will need some work to get them to be in good condition.