Yes, he did use a feeler gauge upon my insistence, but I doubt it was of the correct thickness.
That's quite encouraging, but I am too lazy to do that and I can safely claim the "laziest person on the planet Earth" title. Plus, that famous dialogue from Munna Bhai MBBS comes to my mind "mere hath ki taraf dekho, is hath ne hazaron operation kiye or aaj tak kanpa nahin; magar maen meri beti ka operation karoon ga to phir zaroor kanpe ga". I hope you get the idea 
Well, that was a joke. I would rather leave the job to the experts. The first time I had my tappets adjusted was by Suzuki guys and that was a job well done; I rode out of showroom happily. Why I insist on relying upon the experts is because they have the overall idea of the engine mechanics and know exactly what else might go wrong if they mess up servicing the tappets in particular or any other component in general.
And please allow me to substantiate this with an example. The first time I had the tappets adjusted at Suzuki service center, the mechanic did not open the magnet cover for alignment. He did it entirely based on his experience and training on GD. This road-side mechanic wanted to open the magnet cover, but I didn't let him do that saying Suzuki guy didn't do that either. He agreed and said he'll do the alignment by "kicking" the engine, I said okay. So he adjusted the tappets without me letting him do the alignment using the magnet, and I ended up having my tappets all messed up. He definitely had adjusted tappets of 70 and 125 a countless number of times, but the job got totally messed up on the new engine despite his vast experience on other machines because he did not have any idea of its internals and how it was different from other machines he is an expert of.
Ahhh, I'm short of breath
But I do hope I made my point clear. But thank you, anyway 
Thank you, brother. I have the service manual with me and it has the valve clearance values for each valve as below:
Inlet valve = 0.03-0.08mm
Exhaust valve = 0.08-0.13mm
I'll go to the Suzuki showroom in the morning with high hopes. Let's see what comes out of it.