If only that was how it is done, considering some of the appalling methodology that gets through peer review I think it can be more like...
- Check if the conclusion in line with your personal allegiances
- Consider if it would be beneficial to be/stay on good terms with the author
- Might the author one day review a paper or yours
- Does the paper make any of your own research look bad
- Is there any inconvenient data that the author didn't properly bury or obfuscate
- Could the conclusion be sensationalised to more strongly support preexisting beliefs
- If it generally serves your needs go ahead and rubber stamp your friends work