There can be situations when tracing features using satellite imagery where it can be difficult to determine if a feature exists or not. The best option would be to conduct a survey on the ground to determine the existence of the feature in question. There are situations when the editor is tracing features from a remote location in a different part of the world so ground-based surveys are not possible. In this case, add a fixme tag to the feature. For example fixme=probable building. This enables additional mappers who might have more information to improve the data in the future.