I think the median user starts with quicklisp and then clones random stuff into the ~/quicklisp/local-projects/ dir where they are automatically visible.
Oxidation is a big problem with the harsh no-clean fluxes in many cheap lead-free solder wires. Switching to a rosin flux (RMA or RA) name brand solder should fix that (did for me.)
Metcal have a great big doc on tip care that covers this.
The failure mode that I worry about and would need X-ray to detect is that temporary misalignment will merge/bridge some of the solder balls.
I like to "wiggle" the chip with tweezers (under hot air) to see surface tension in action and judge whether the balls have all melted, but a tiny bit too much wiggle causes that problem.
