Our app has been rejected (twice) due to the external market links policy, this is the message we have received from slideme:

*EXTERNAL MARKET PURCHASE LINKS: SlideME operates and is present on most
devices without Google Play or GMS-enabled. Redirecting users from a free
application version available on SlideME to purchase a paid version (to
include unlocking, removal of ads, pro features, donations, non-optional
premium content, etc) on another store, or otherwise "teasing" users
regarding a full/pro version or other paid features that they cannot access
is a violation of the Developer Distribution Agreement you agreed to when you
submitted your application. As such, if you choose to do so must also submit
to SlideME the paid version of your application or provide a fully featured
version (with ads allowed) containing no purchase links or disabled
references that tease other features they could have if they used Google
Play. Only optional purchases (such as virtual currency, time-shifting,
non-necessary items) are permitted through other application markets.
Full/pro/paid features/ad-removal purchases are permitted through non-market
options such as PayPal or other mobile/SMS-based billing (such as Fortumo).
Note that if you have a full version with more features on another market,
you must also provide all of the same features on SlideME (though with ads is
permitted). Simply providing only less-featured lite versions to SlideME
users will cause your applications to be rejected.

While it is true that we offer an option to remove ads through the use of Google Play in-app billing, this is completely optional and we do not redirect, "tease" or offer the option to remove ads on devices where we fail to connect to the Google Play Billing service. To be clear, the option to remove ads (a menu item on the home activity Action Bar) is only visible on devices where Google Play Market is available. Are we not allowed to use Google Play billing at all, even when it is available?