I think it is all too easy to imagine the nuts and bolt of either a battery swap or battery repair, and think "not much to it, I can do that"! 1st is a safety issue, working with HV DC is not like changing the 12 volt battery, it can and will kill you if you mess up. That is why PPE and insulated tools are a must.
None of that comes into play if you just drop the whole pack out and install a new one, but, you can damage the pack if you don't support it correctly, you need to make a cradle to support the pack and lift the car off the pack, not drop it down with jacks.
Dala is a well respected member here and has solved many problems with doing pack swaps and other issues. Look at his videos about his 64Kwh pack install. Yep, even he bought a pack that was damaged from the get-go and had to repair it. He has the tools and knowledge to do it safely, but still it wasn't a straight forward, un bolt-re bolt swap.
I have made my living doing repairs for 50 years on all kinds of mechanical stuff, there is very little I am not going to tackle, and that includes diesel fuel injection and hypoid gear sets. I have done all that and more.
True the mechanics of HV battery work is not complex, but it does require stuff that most, including myself don't own. To "kit up" to do battery work for one car makes no economic sense. The PPE and insulated tooling alone will cost you dearly, then add you really need a lift table or hyd lift to remove the battery without damaging it and you have exceeded to cost of a new battery just getting to the point of being able to "do it yourself". The add to that the learning curve, even Dala had to take his out at least twice, and that price quoted to have it done looks better and better. Add to that you have recourse if something goes wrong, you don't if you buy from auction and find out it doesn't make the car any better.
Fine, if you want to set your self up to do many cars for hire, I would encourage that kind of business, we need more that can do the work if electrics are going to be viable in the long run.
Those who bought a cheap 2nd hand Leaf find that they can be had much cheaper with much fewer miles on them than hybrids and ICE cars. Where some go wrong, is they expect the battery to be able to be repaired or replaced equally as cheaply as the bought the car. When they find it isn't so, they are upset that replacing with a new battery cost more than buying another used cheap Leaf. If you like the car, and want to keep it, then invest in it. Yeah it will cost about the same as buying a similar year/mileage hybrid when your done, but you'll have an electric. There is no free lunch, and if you based your purchase on the car price alone, without doing research, you will be disappointed.
, and will be listening on line to hear how it worked out. At this point I think that late model low use battery packs installed by a competent shop are the best you can do in the US. Keep us informed about what direction you choose and how it works for you.