There\'s a good report here of a recent scam perpetrated through the Android market.
http://www.theregister.co.uk/2011/12/12/android_market_malware/
Someone
If you are willing to spend some money then go for some professional help such as Arxan. We have used this in our enterprise level app. Basically it recompiles the .apk with its own encryption and creates a new apk which will enable you to know whether tampering was done with apk and other such instances. You may refer to this url : https://www.arxan.com/ for more details and do your research accordingly.