There will always be some discrepancy between sessions and clicks, but bounce rate for example isn't measured by Google ads, it's imported to Ads from analytics, so not sure why you would see a discrepancy there. Conversion discrepancies can be your attribution mode being different in ads or one of the codes failing to fire occasionally. Finally, if you're concerned about click fraud, try something like clickcease or PPCsecure. Neither are perfect but they will have a measurable effect in reducing your invalid click rate, while clickcease will also submit refund requests directly to Google on your behalf every 2 months (potentially making the tool free). How large are these discrepancies?