When my business was suffering because of the recession in 2007-9 (uk) I bought up full systems from eBay and sold all the parts / livestock on forums and ebay
I converted my garage into a fish room , racks with 12 tanks for fish , a live rock bin , 8 foot coral tank and another 12 foot fish tank for the bigger ones
All the parts and tanks were cleaned up and advertised
I must have bought up 100 in those 2 years all like 1/5th the cost of everything from a shop so basically tripled my outlay
It was very successful but backbreaking with those 8-10 footers which were the best for profit cos they were struggling to find anyone willing to take on the task
The good thing was that losses were minimal cos the corals and fish were from established tanks and were hardier than freshly shipped
Incidentally , my wife just left and took every penny with her and was looking on eBay here in Portugal to maybe do it again
It was easy but you had to be well equipped for the 500 mile round trips you had to sometimes do