How can you tell that you put the o2 sensors on right from upstream and downstream?

To verify that you installed the O2 sensors correctly, check the wiring and connectors: the upstream sensor (pre-catalytic converter) typically has a different connector or wire length compared to the downstream sensor (post-catalytic converter). You can also refer to the vehicle's service manual for the correct placement and specifications. Additionally, after installation, monitor the vehicle's diagnostic system for error codes related to the O2 sensors; if there are no issues, it's likely they were installed correctly.