Lets just not forget third party solutions abuse the Google policy.
Not true,
It all depends on what you are accepting the payment for.....
Sure if you use Zooz or Paypal for unlocking app features, or selling digital items in a game, yes, that's not smart
but, If you are a post card printing company, selling 500 postcards for $20, you are not going to give away 30% to google for that order.
It's bad enough you have to give away 3.5% to 4.5% of that order with paypal.....
for the $20 order the break down would be something like this:
.70cents + .30cent fee = $1.00 to paypal
vs.
$6 to google
they know that is not fair, and this is where they allow you to use other merchant processing in the app (physical goods or services)
===
Paid and Free Applications
In-app purchases: Developers offering additional content,
services or functionality within an application downloaded
from Google Play must use Google Play's payment system
as the method of payment,
except:
where payment is primarily for physical goods or services
(e.g. buying movie tickets; e.g. buying a publication where the price also includes a hard copy subscription); or
except:
where payment is for digital content or goods that may be consumed outside of the application itself (e.g. buying songs that can be played on other music players)
Developers must not mislead users about the applications they are selling nor about any in-app services, goods, content or functionality they are selling.