Why is the tech not paying for it...?
Meh, I mean keep in mind it was an 80 Euro deal. Would be a risky venture if any chance something went wrong, you were footing the bill for hundreds of dollars more than you were getting paid because your customer got to choose who fixed it and how.
To the OP, total sympathies on the whole thing and tbh, I don't blame you for how you handled it (including running off in a rush without a receipt). Fwiw, I can understand distrusting having another tech/luthier do this kind of work again but it IS an accident that happens, so you're just as likely to make the same mistake. If it's just about the peace of mind and not having to pay if something DOES get fucked up, I can understand that. Just some food for thought.
Anyway, I think the bigger issue is how the tech resolved this. The repair job was lousy (especially the wandering drill bit), and he shouldn't have charged you anything, that's the start. If he was competent and this did happen, he could have reglued the chip and hidden the seam better, and if necessary (especially the wandering drill bit), he could've sanded it out and reshot the clear on the back. I'm not necessarily down for expecting the guy to swing hundreds of dollars in repair fees but if he's a competent repair guy, he should have swung the extra few hours and materials to do a legitimate fix.
Which brings me to my last point, which is a pet peeves about small repair operations that don't have the resources to fix something like this, if it DID happen. Even if all you do for a living is changing strings adjusting action, there's a mountain of shit that can go wrong on a customer's guitar. If you don't have the tools or skill or whatever to fix it in house, at least have someone you work with who does.
No blame on the customer here at all but I've always thought this was stuff you need to be watchful of when picking your tech, otherwise it's always "buyer beware".