Sadly the knock offs are so close you just can’t tell photographically that well.
The only way I can tell is side by side comparison with a known real unit and the second test is the way the MagSafe LED fires off. [https://beetstech.com/blog/oem-magsafe-chargers-vs-counterfeits-teardown-for-truth|OEM MagSafe Chargers vs Cheap Imposters: Teardown for Truth]
As hard as you might it will likely take you two to three attempts to get a real unit as ther’re just too many out there. Don’t forget Apple is no longer aggressively fighting the importation of chargers anymore as they’ve moved to USB-C chargers.
So the bottom line: Add up the shipping costs and they will likely hit you with a restocking fee its it worth the aggravation trying to save a few bucks and the delay.