I think transparency is key. If Drew Estates or Arturo Fuente started doing podcasts, I'd more than likely sign up. In fact, I would expect/hope that they'd have further insights into their topics than someone doing a podcast for fun.
If they sponsor a podcast, I would expect/hope that the podcaster(s) would (near the top of the show) would thank the sponsor and do their little ad message. I have no problems with that. It's like listening to the Adam And Dr Drew show - they are always suddenly dropping in notes from their sponsors.
I DO have a problem when a podcast is sponsored but never mentions it. Even if they are not influenced by the sponsorship, I would have a hard time accepting their credibility if I knew they had hidden their sponsorship.
My podcast isn't sponsored at all so I don't have anything to reveal. But I have received sponsorship from a few manufacturers in my photography business and I do let people know about that when it's appropriate (there is a line between disclosure and bragging :eyebrow: )
As for receiving compensation of any form to do a review... I find that to be ethically, I dunno, "murky"? It happens all the time and, again, I think transparency is important. If I receive a piece of equipment, asked to do a review, then told I can keep it afterward, I'll tell my listeners/readers that and will still do an honest review.
I also send the review to the manufacturer because sometimes there are some minor adjustments they could make to the product and I'm happy to provide my opinion.
To sum that all up - transparency on behalf of the reviewer and how (s)he handles it determines - in my mind, at least, the level of credibility.