I think the assessment of how good this refinishing job is going to vary, and this subjectivity may lead to the Question ultimately being locked. However I think at least part of this isn't purely subjective....
Can you tell me if this is adequate workmanship?
I think this is a good question to include since it can be assessed fairly objectively. And the answer is a definite no.
the quality of the work seems like shit.
As the client, really your opinion is the most important one. And if you think it looks like shit then that pretty much sums it up; nobody should get back a piece of furniture after a professional has done their work and have any legitimate basis for thinking this. And while I'd want to see more of the dining set to get a better overall picture, from what we can see in the images I'd be inclined to agree with your assessment!
I'm shocked at how bad this is in a few areas, not least given the quoted cost.
I wouldn't be surprised to see work of this (low) calibre from some of the hobbyist refinishers/furniture flippers on YouTube. And there are at least a handful capable of much better work than this.
Some specifics issues:
The cross-grain scratches
These are visible in at least two images and I'd guess they're more widespread; to put it bluntly these are a sure sign of amateurish or outright inept workmanship (depending on whether they were there to begin with or not).
No person engaged in this work who is calling themselves a professional should create scratches like this; it is pretty literally Sanding 101 to learn how not to do this!
But, what if they were there to begin with? It is by no means a gigantic task to remove them, without it taking a long time, if you know what you're doing. So IMO it is amateur hour to leave them, unless a prior agreement was made specifically stating there would be no surfacing work or something along those lines.
This is the worst part of this I think. Although I can visualise a possible cause in the workshop I can't imagine anyone but the most amateurish leaving them if they were responsible for causing them1 .
One quick thing in relation to something you said later in the Comments.
"Refinishing" doesn't automatically mean a complete removal of finish down to bare wood and application of fresh finish, although of course the full monty can be specified in advance.
There are levels of intervention, which (often) lead to only partial refinishing in the literal meaning of the word2. There are legitimate cases where spot-refinishing or refreshing of the existing finish is the right call, based on finish type (easiest with shellac or traditional lacquers), an assessment of condition, and budget.
1 There are just certain things you can't accept if you call yourself a pro, even if it ends up costing you.
2 On tables for example it's very common for only the tabletop to be refinished (and sometimes the top surface only, and not the four edges), with the understructure and legs to only have light touch-up work done to them IF needed, only cleaned and polished if not needed.