The main faults liable to be encountered appear to be:
The skills required in dealing with these faults are probably mostly ‘mechanical’ though the expertise required when tackling larger bodywork celluloid repairs is definitely specialised.
Since a lot of information on bodywork repairs is already in the public domain it is not intended to repeat the information here. A very useful book on the subject is ‘Accordion Repairs Made Easy’ by John Reuther which is published by Deffner of New York or ‘The ins and outs of the accordion’ by Thierry Benetoux – click here for more details.