Only after establishing what the payment buys and whether it is refundable. A reservation secures a subscription slot in a commercial offering; it purchases no immigration position and no priority with the government. Ask for the refund terms in the document rather than in an email summary, and check what happens if the applicant later declines.
Total the cost of comparing, then of proceeding
Due diligence itself costs money: independent legal review of each offering, translation, and any commercial or accounting advice sought at home. Budget that separately from the capital, and decide how many projects are worth reviewing at that price. Once a project is chosen, add government filing fees, family processing, medical examinations and administrative charges levied by the sponsor.
Ask each adviser for a written scope so later work is not assumed to be included. Decide in advance how much comparison the applicant is prepared to fund, since independent review of three offerings costs three times as much as review of one and the third rarely changes the answer. A workable approach is a short screening pass on all of them against the comparison sheet, followed by a full review of the one or two that survive it.
Ask each adviser for a written scope so that later work, including responses to any government request for evidence, is not assumed to be included when it is not.