Will the out-of-pocket expenses charged by professionals to claim reimbursement of expenses incurred by them for rendering services to their clients be included in the transaction value

Yes. Any expenses incurred by the supplier relating to supply until the services are delivered, and which are charged to the recipient, will have to be included in the transaction value.

(ICAI FAQ PUBLICATIONS 06-09-2017 VALUE OF TAXABLE SUPPLY: FAQ NO. 59)