JDavis;
Yours is a legitimate question/issue. I will try to answer as best I can. Most established outdoor writers receive steep discounts or totally free products. I believe most would be ethical enough to not let that color their endorsements, but am not so naive as to believe it never happens.
I do think overall our record is pretty good. For example, established writers can get Loomis, Lamiglas, Sage and other rods at a major discount or sometimes for free. Given that they can choose whichever brands they wish to use it seem likely that they choose the one they like best and naturally would recommend that product.
Almost all line manufacturers will give established writers line for free. (Similar programs are often offered to top guides as well.) I have recently recommended Berkley Ironsilk, not because I get it free, but because I really like it.
I often recommend Dick Nite spoons, which I buy at retail. I recommend them because they work.
I do not know whom you were referring to regarding the flashers, but can't imagine too many guys willing to sell their soul for a handful of free flashers. But I know such things do happen. I guess like in anything else you need to do your own homework and remain a bit skeptical.
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No huevos no pollo.