Interior designers have legal problems for many reasons. The most common issue is when they don't follow a schedule. Projects often have delays and setbacks, but if when they get out of hand, the designer could be sued.
If a designer gives false information to their client, they might get sued.  Making small changes to an original plan and failing to alert the client could cause legal problems. Also, changing building materials, like flooring or roofing, would be grounds for a lawsuit.