Based on your previous posts
@carmen617 you've got the basics down pat. Unfortunately, due to Apple's attitude, there is no really reliable aftermarket repair for their machine's as there is no reliable source of OEM parts. Also, do you have tools like Disk Warrior and Tech Tools Pro? They are reasonably priced. And DW does wonders with file system problems.
The reason I recommended unplugging the battery is that tends to interfere with an SMC reset. Apple's instructions for
resetting SMC on laptops assumes an EU, not a tech. Even with laptops with no EU removable battery a tech can pop off the back and disconnect the battery.
Yes, they got their money's worth out of this machine. Going forward? If possible give it a little more test time. Give it a bunch of reboots and shutdown/power ups. A couple more AHT's in between. Those models are pretty reliable. Then move to usage patterns. The problem with many notebook users is they tend to just close the lid rather than shutdown. I've seen this problem with W10 laptops as well. They will store info in the hibernation file which gets corrupted and prevents a proper boot. If things look good then there should be few problems going forward and it should be good until the next upgrade.
Personally I'd discuss a possible upgrade if they want to keep the machine. I really like these as they have more ports as well as an opti drive. I've upgraded an original purchase, 2011 13" MBP, as well as a recently purchased used machine, 2012 13" MBP, to SSD and maxed the RAM. Boot times are within a few seconds of a top of the line MBP Retina. The good news is they use standard SATA connections so the drive price is much lower than M2's, etc.
What to charge? Not sure of your pricing structure. If it was me I'd be looking at something like $100 with a 30 day guarantee. Best of luck!