Andel is regulated under slightly different laws, technically you own shares in an ownership association with a right to use a specific apartment in the assocation. The main thing to look out for practically are restrictions in the articles (vedtekter) eg regarding renting out or if other owners have a right of first refusal (forkjøpsrett). Looking at mutual debt (fellesgjeld) levels is another thing worth doing. I’m not sure they are more difficult to sell generally, though some people can be initially sceptical and ask questions. The property broker should be able to give you (and others with the same questions) good answers so you should not hesitate to ask them.