Keep data and results credible and accurate.
Learn how each one defines and measures sessions, users, conversions, and so on. Understand the reporting discrepancies between them. For example, Google Analytics and VWO, limit a conversion to once per session or visitor, while Optimizely allows you to count each conversion.
The comparison range shouldn’t be from too far in the past. The previous month or last 30 days is generally a safe pick.
For instance, there’s not much point in comparing sessions to users, or unique conversions per user to total conversions.
For example, knowing that you have a 15% difference in overall transactions doesn’t tell you much. Knowing that 100% of all PayPal transactions are missing, however, is much better.
Go through funnels yourself to make sure certain events are indeed missing, broken, or that something else is off.
Don’t start editing, adding, or removing tags or snippets, without proper knowledge of how the tools work to avoid turning small discrepancies into massive ones.
In most cases, fixing discrepancies requires some work by developers, analytics implementation specialists, or other experts.