Suggest your client not waste time calling "them" back.
For their magic process to work, spices and terminations would have to be blistering hot, and there will likely be other complaints before that point. Think about this for a bit—it makes good sense.
You can prove it to yourself with a POWER-RATED multimeter on a low-range AC-volt scale. Voltage drop can be carefully but literally measured across cable-to-lug joints—then multiplied by the current through the joint. Roughly, millivolts x amperes = milliwatts of power dissipation in the joint.
{A reference is
http://ecmweb.com/ar/electric_testing_contact_quality/index.htm Testing Contact Quality on Live Motor Starters—based on another short EC&M article by me; published in the mid 1990s. A similar discussion is
http://ecmweb.com/ar/electric_troubleshooting_electrical_problems/index.htm A significant advance in a number of multimeters is that appropriately-rated meters will not be damaged by accidental application of line voltage while in a millivolt range: this makes the technique workable.}
