If it was sold as "used" and without any expressed caveats, and when you received it was not working as one would expect a good used laptop would work, then I think you have a fair case for return using the principle as not-as-described. I'd go into your eBay Purchase History, choose "Return This Item", and then select "Not As Described".
I wouldn't put any focus on the fact that there is an aftermarket SSD inside - used computers have often been altered since their manufacture. What's important here is that the laptop doesn't work as a reasonable buyer of a good used laptop would expect.
If it is a "user" issue (you did an upgrade or dropped it or ? that led to misbehavior of the machine), then as a seller I'd be concerned that the buyer manipulated the machine and now as a seller I need to eat a lot of costs and take risks due to an wild-west buyer.
Generally I find simplicity the best course of action. Avoid rants and diatribes, and instead say "not as described" - Detail: "laptop is unreliable: crashes consistently at wake, requiring frequent reboots".
