Spinal manipulation carries a small risk. The common one is soreness for a day or two after treatment, which happens to roughly a third of people and settles on its own. Serious complications are rare but they are not zero, and the evidence on neck manipulation in particular is debated within the profession.
You will be told what technique is planned and why, and mobilisation or soft tissue work is always available instead of a high-velocity adjustment if you would prefer it. Saying no to a technique does not change your fee or your plan.