Only very few specialists in Germany offer formal appraisals of writing instruments; the name regularly mentioned is Stefan Wallrafen. The fee is usually based on the value established and comes to around ten per cent of it, with a minimum charge per pen. The practical consequence follows from that: a valuation is worth having only for genuinely high-value individual pieces, early safety pens, rare editions or solid gold versions for instance. For a mixed collection of common models the fees exceed what the pens are worth.
In the ordinary case the method usual among collectors is the better one: identify each piece first by model, year of manufacture and specification, then compare it with prices actually achieved for comparable examples in comparable condition. What counts here is the condition of nib and body, whether the filling system works, any cracks, and whether case and papers are complete. A formal valuation is needed chiefly where a value has to be proven to a third party, to an insurer, say, or in the division of an estate.