Is Google Scholar reliable for reporting citations? When quoting the number of citations for each paper you have published, different sources can be used, Google Scholar, ResearcherID, Scopus.
Google Scholar covers a larger range of literature.

Is it acceptable to use Google Scholar? Or it is not a professional resource, and we necessarily should use ISI Web of Knowledge for counting citations?
None of the citation databases are particularly good.  Google Scholar tends to err on the side of inclusiveness (thereby over-representing impact), while the more curated databases (e.g., ISI WoK) tend to err on the side of exclusiveness (thereby under-representing impact).  This is particularly acute in some fields: computer science, for example, is notoriously under-represented in the curated databases to the degree that it has is own independent citation database, DBLP, which of course has its own different problems.

You can potentially use any of these databases reasonably to report citations in a reasonable and professional manner, as long as you are consistent and make it clear which database you are using, such that readers can adjust their expectations accordingly.