Yes sir, there is no doubt Josh Duggar used the service. There are transactions that prove it. When this broke, it was the financial transactions that proved their validity.
And in the same breath, it is the lack of financial transactions that prove this is a false story regarding Cruz. I've read a lot of the paid for social media posts by the Trump campaign. They post something that gets retweeted etc by their grouped accounts and then average Joe starts sending it around without validating the facts. This is one of those situations.
There is no transaction required to sign up for that site. To use the service, yes. To sign up, no. You can make a user name and sign up under Mother Teresa's email. But that doesn't mean Mother Teresa used the service.
https://www.ashleymadison.com/m/login