I have no problems with Avast showing ads for their paid products.
If you disable "Show avast recommendation features" and "show social networking features" in Settings, then you also will not be notified about Avast free promotions, giveaways and discounts for their paid products.
I won two free 1 year subscriptions for Avast Security Suite giveaways from those ads!! Because I'm not going to complain.
The notifications usually are for only promotions and discounts much cheaper than if you bought their paid products from their site or third-party resales. Clicking the links will give you there special promotional, giveaway and discount pages not shown on their website.
Avast provides the only free antivirus not limited in protection features and completely user friendly.
Their developers have to get paid for their work, they have families to take care just like anyone else. The costs of development is not cheap, especially having to keep up to date with the latest threat signatures, maintenance on their web servers, etc.
Avast doesn't ask for donations, the only source of income they receive is from their paid products. They don't bundle rogue products like many other AV vendors do to support their costs. They don't publish fake reports for adverts like most other AV vendors. They run one of the cleanest businesses in the antivirus community, they don't use any sources known to be rogue or misleading. Buying their products helps support the development and keeps Avast free.
So if the ads are too much for you to handle then either buy one of their buy products or use another free antivirus with limited protection.
Thanks.