Yes, it is generally safe to cook in a microwave oven that has been used by someone else before you. Microwave ovens are designed to be used by multiple users, and as long as the oven is clean and functioning properly, there should be no significant health or safety concerns.
However, it's always a good practice to ensure that the microwave oven is clean before using it, especially if it has been previously used by someone else. Wipe down the interior with a damp cloth or use a microwave-safe cleaning agent to remove any food residue or spills. Pay attention to any specific cleaning instructions provided by the manufacturer in the oven's user manual.
By keeping the microwave oven clean, you can maintain good hygiene standards and reduce the risk of cross-contamination or the transfer of unwanted flavors or odors between different food items.
If you have any concerns about the cleanliness or functionality of the microwave oven, it's advisable to inspect it or consult the owner or maintenance personnel for further assistance.