Can I contact your past clients to have their opinion?

I am afraid it is not possible.
As most of our clients are private users, it is our policy not to use them as a reference.
Arranging a meeting between an old customer and a perspective client may be time consuming, may be invasive of the privacy and we just have not the structure to be able to take responsibility for any trouble or miscommunication.
As we cannot be on site to manage the situation, we cannot refer past clients and we make no exception to this policy.
Thank you for your understanding.