Most subletting problems are visible in advance. Nine questions that are awkward to ask and cheap compared with the alternative.
The most important question is also the simplest: does whoever is letting have permission to do so? A rental flat needs the landlord's approval, a bostadsrätt needs the association's. Without it you may have to move at short notice.
Also ask what happens if the primary tenant comes back earlier than planned, and get the answer in writing. Verbal agreements about moving out rarely hold up when they're needed.
And check the rent. For a sublet rental flat there are rules on how much may be charged, and if you pay more than that you may be entitled to the difference back.
