Yep, you can set up one off or recurring payments for "User Upgrades". Once they've purchased your upgrade, they will be promoted automatically to a new usergroup which can, for example, not display any ads.
On that note, XenForo's template system is awesome.
Firstly, there's special templates (by default, blank templates) that are designed for adverts. So many common placements such as ad_above_top_breadcrumb (Above the top breadcrumb) ad_below_top_breadcrumb (Below the top breadcrumb navigation). There's lots of them for you to choose from, they are all prefixed with ad_
Obviously you can put advert code in whichever template you like, but these are specially designed for the purpose so you just copy and paste your ad code into them.
With regards to hiding the adverts from your paid users, each usergroup will have a group ID. Registered users, for example, are user group ID 2.
If you create a usergroup called "Ad Free Users" and this is where your paid members are put and if we assume that usergroup ID is 5, you can place this in your templates to hide the adverts from these users:
That's perfect, I played with a demo yesterday and placing my advertisements was easy... Everything I have seen so far is easy. I actually have 2 forums, one is a sports forum with about 1000 members but the activity is kinda slow over all and I don't want to dump a bunch of money in it because that's a hobby site. I want something that is simple, fast and stable... And especially want a system when flaws are detected , patches will come out in a timely manner as paid software should.
It's always a risk buying a software and then getting buyer's regret. If you're having second thoughts then obviously hold off for a while but it's a great piece of software and i doubt you'll have regrets. If you do decide to sell it you won't get much for it i'll say that now, I've seen xenforo licenses go for as little as 30-40 dollars But you may get a good price for it if you decide to sell.
I doubt that will be the case though, but thought i'd post the reality of selling second licenses aren't worth much. Also, you would have to wait 140 days before selling it. Might actually be 120 days before you can sell a license maybe somebody could clarify that.