Ok, folks. Chat went as follows:

Ricardo Xavier
12:34:30 Hi. I purchased a Galaxy S8+ last week from Amazon UK. The seller was Samsung. Everything seemed fine, until I started suspecting this might be a clone/ replicate phone. The reason for this is that Antutu Benchmark app is giving my phone scores way lower than the S8+ they have listed in their database. The name of the phone also doesn't match their data, in which mine has a funny, perhaps chinese character in the middle of the name. I'd like to know from you how do I check if my phone is legitimate.
Sam
12:34:32 Welcome to Samsung Support. Please allow me a moment to read through your enquiry.
12:35:12 Hello there, I hope you are well
Ricardo Xavier
12:35:27 Hello, likewise. I am, thank you very much.
12:36:12 I'm sorry if this issue sounds silly, but I'm seriously concerned so I wanted to hear what you guys think.
Sam
12:37:13 Since we are Samsung UK, we can only troubleshoot EU devices. To check if this device is EU, please may I have the Serial and IMEI numbers of the device?
Ricardo Xavier
12:38:01 Sure thing.
12:38:47 xxxxxxxxxx - IMEI
12:39:13 Where do I check the Serial number?
Sam
12:40:09 This would be on the back of the device in smallprint as well as in Settings>About Device>Status
Ricardo Xavier
12:40:23 Thanks, one sec.
12:41:02 xxxxxxxxxx
12:41:49 But yes, the device should be UK as I got it from Amazon UK and Samsung was the seller. Supposedly region-locked.
Sam
12:42:25 Yes I can confirm that it is an EU device
Ricardo Xavier
12:43:01 So this device definitely came from you guys and there's nothing fishy about right? Nothing for me to worry about?
Sam
12:44:57 There is one more thing you can test if you follow these steps: 1. Turn the device off 2. Hold down Power, Home & Volume Down 3. This will bring you to a downloading screen, press Volume Up to continue 4. You should see the following headings: 'System Status', 'Current Binary' and 'Knox Warranty/Warranty Void'. Please let me know what is displayed after each heading.
Ricardo Xavier
12:45:30 Thank you for your time, one min.
Sam
12:46:08 Sure
Ricardo Xavier
12:48:06 Huh I can't seem to do it, probably because of the lack of a physical home button now. Does the pressure still work?
Sam
12:48:40 Ah, please bear with me whilst I get more details
Ricardo Xavier
12:49:05 Oh I got it no worries.
12:49:11 It was the Bixby button aah.
Sam
12:49:29 Yes, apologies for any confusion
Ricardo Xavier
12:49:37 No worries. Let's see...
12:49:50 Sys Status: Official
12:50:10 Binary: Samsung Official
12:50:23 WARRANTY VOID: 0
12:50:28 This looks fine.
12:50:52 Reckon that's enough to confirm the device is good and there's no way to replicate such thing?
Sam
12:51:14 Yes that confirms the device is genuine. Thanks a lot for those details, much appreciated
Ricardo Xavier
12:51:26 Thank you very much for your time and help.