Short answer: There is no legitimate third-party fee that can buy or guarantee Web of Science indexing. A company may charge for editing, journal-policy review, publishing-process consulting, or publisher readiness work, but the Web of Science evaluation decision belongs to Clarivate.
For authors, the practical service is usually journal selection or manuscript preparation—not “indexing” the author’s paper. Journals are evaluated for coverage; individual manuscript acceptance is handled by the journal.
For publishers, consulting can help review public criteria and improve editorial processes, but only the journal publisher can submit an evaluation request through Clarivate’s Publisher Portal, and Clarivate makes the decision.
Before paying, ask for the exact deliverables. Avoid contracts that describe the fee as payment for guaranteed Web of Science inclusion.
Official reference: Clarivate journal evaluation process.