Always check the edges and base thickness when taking equipment in, make sure there is enough material left to tune. New edge material is generally between 1.5 to 1.8 mm; if there is less than 1.0 mm, tune with caution. Also look for discoloration in the base, usually in the tip and tail area. Make sure to advise the customer if any problems are seen and what could happen if you tune through the base material. If the ski/board looks like it is worn out, suggest they walk over to the new ski/board wall. If they still want to get a tune make a note on the repair ticket and have them sign it before leaving. It's always easier to cover this with the customer before you take the equipment in than after the fact.

Base and edge thickness
Base thickness of retail ski 0.8 – 1.2 mm
Customer skis can be ground about 20 x assuming a base thickness of 1 mm (material removal per service ~ 0.05 mm)
Base thickness of rental ski 1.0 – 1.6 mm
Rental skis are ground about 50 x assuming a base thickness of 1.2 to 1.4 mm (material removal per service ~ 0.02 mm)
The raw, undressed edge has a thickness of approx. 2.0 mm
The edge on a new ski has a thickness of 1.5 – 1.8 mm
The usable surface is approx. 1.0 – 1.3 mm