I try not to worry too much about the credibility thing. People are right to be skeptical of just about anything but...
First... yeah, always seems to be some drama around Tekton. Could be because the company publishes some audacious claims about the performance of its speakers.
OK, so just some thoughts...
1. An established professional reviewer probably already has a system they like. Hoarding gear or getting steep discounts is not a realistic motivator.
2. I get paid a salary, not per review. But I can see how for a freelancer, a larger paycheck could be a motivator to "sweeten" a review. But in the end, ethics are what matter.
3. If you give negative reviews often, not only will the supply of review gear dry up (you'd have to be monumentally naive to believe otherwise). But it also implies either that you can't pick decent gear to begin with, or that you actually enjoy listening to bad sound for a living. I don't fit into either category.
4. Some of the best, most liked brands advertise here. Am I really supposed to turn down SVS Sound when a new sub comes out? Or Paradigm? That's just not gonna work. I pity the for-profit enterprise that has such a policy, I presume they all went bankrupt long ago.
5. Regarding industry accommodation pricing, consider the following: Once a review is done, that gear is no longer new. It's used and has to be sold as open box. The packaging takes a beating. Furthermore there is a cost involved in shipping it back, which with speakers can be considerable. So yes, companies offer a discount to the reviewer since that's the shortest path to solving the "what to do with these used speakers" issue.
6. As for keeping gear for months... It's funny but sometimes I do keep gear for months... in a box! Mostly because I'm busy with other reviews. Sometimes because it takes a while just to get return labels. But another school of thought is that you really do need time to get to know a product, you don't necessarily want to base a review on first/early impressions.
7. Influencers are a whole different situation. But I will tell you this, if I had a million followers on YouTube and the income that kind of audience can generate, I would in fact quite my day job.
Alas, I don't think I'm cute or funny enough.