Oddly enough, I've had interviews that I didn't feel went well - and been offered the job(s), and interviews that I thought went very well, but I didn't.
Preparation and effort are still important, I feel, even in this day and age. Research and actually showing you've got interest and have made some effort.
As you've experienced, there are people who aren't very good at it, don't want to be doing it, perhaps are only going through the motions. But then there's something of a true-ism, there - many in work situations are put in positions they're ill-equipped for - or perhaps really don't want to be doing - yet it's dumped on them, and sometimes the just-in-time training / coaching / mentoring isn't just-in-time or anywhere sufficient- or perhaps totally non-existent.
Reading books on technique and body language can be helpful - it can help you appear at your best, as well as helping you read the situation.
I always think of an interview as a two-way thing - an opportuinity for them to find out about you, and you to sell yourself to them - and the reverse, and opportuinity for you to find out about them and for them to sell themselves, too. I always think that the psychology of the situation is probably best for you if you can maintain the perspective of it being just as important for them to sell the position to you too (even if it's not fully true - even if you'd snap their hands off for the job, or you just really need it).
Good interviewers try to have more of a conversation with you - to keep some flow going without it being / seeming artificial - so be aware of that, in how you respond - if you feel that they are having to go back to an agenda or list of questions, it may be they're not very good at it, or it may be that the interview isn't going to well, and perhaps you're not providing enough for them to tease out more things as it progresses.
In contrast, some interviews are very structured - the quandrant type assesments, and similar things, where their process requires much more of a recipe to follow. Remember in those situations, what they're looking for isn't how perfect you are, they are looking for all aspects - self-realisation, things you do well, but more importantly, things you don't do well, or could improve on - they may well want to see / understand how you deal with that, and how you respond to need to improve or develop something.
One other thing - when it comes to questions - ask some - even if there's not that much you don't know or understand about the job - ask them things that are a little challenging - in the same way as you'd not expect them to try simply stump you, don't do that - but ask them things like "What makes this a great place to work?" "What would you say to somebody to persuade them to work here?" "What do you like most about your job?" "What do you like least about your job?" - things like that help the psychology of the situation (more for you than them) but also, can be very revealling.
Personally, when I've being interviewed for a job I'd consider, I'd want to know what the interviewer thought about working there - why I should want to, and maybe some of the downsides.