Web forms are a common way for web service providers to collect data from their users. Usually, the users are asked for a lot of information while some items are labeled as optional and others as mandatory. When filling in the web form, users have to decide, which data, often of personal and sensitive nature, they want to share. The factors that influence the decision whether or not to share some information has been studied in the literature in various contexts. However, it is unclear to which extent their results can be transferred to other contexts. In this work we conduct a qualitative user study to verify, whether the reasons for sharing optional information from previous studies [12] are relevant for the context of interacting with a commercial website. We found, that only a few of them were named by the participants of our study.