What kind of issues do people conceal?
1. Battery puked out pretty quickly, so that's $100 (AUD) to fix on a $500 second hand laptop.
2. Some keys stopped working, could be bad luck as laptops have shite keyboards normally.
Both are not necessarily concealed issues BUT this is the kind of shit you are dealing with with second hand laptops and the savings don't seem to justify it, for me anyway. Plus less NSAWare.
The main benefit of buying second hand is the 'good for the environment' feeling it gave me.
While a refurbisher could potentially insert malware, they're not going to do it for the NSA.
Old Thinkpads are also generally well supported by libreboot/coreboot, so that's one less attack vector to worry about.