You can't have it both ways. If you're writing reviews that are read by "thousands" and you are receiving discounts on the products you review, then that is a material connection to the manufacturer that must be disclosed. And you're not doing this for free. If you receive a discount, then you are in fact being compensated to the tune of the amount of said discount. People may be making buying decisions based on your reviews (for better or for worse). Accordingly, you have a duty to disclose anything that might affect the credibility of your review. Fortunately, this is all rather easily solved by simple, clear, conspicuous disclosure. When people balk at such disclosure, I get very, very suspicious about motives. But who cares what I think. The FTC on the other hand...
I recommend familiarizing yourself with the FTC's 2009 guidelines on endorsements (attached hereto) and the recent guidance it disseminated regarding same. The FTC has made it very clear what the rules are and how to comply. I'll get you started. Example 7 concerning Section 255.5 seems particularly apt to me:
Example 7 (section 255.5 disclosure of material connections): A college student who has earned a reputation as a video game expert maintains a personal weblog or “blog” where he posts entries about his gaming experiences. Readers of his blog frequently seek his opinions about video game hardware and software. As it has done in the past, the manufacturer of a newly released video game system sends the student a free copy of the system and asks him to write about it on his blog. He tests the new gaming system and writes a favorable review. Because his review is disseminated via a form of consumer-generated media in which his relationship to the advertiser is not inherently obvious, readers are unlikely to know that he has received the video game system free of charge in exchange for his review of the product, and given the value of the video game system, this fact likely would materially affect the credibility they attach to his endorsement. Accordingly, the blogger should clearly and conspicuously disclose that he received the gaming system free of charge. The manufacturer should advise him at the time it provides the gaming system that this connection should bedisclosed, and it should have procedures in place to try to monitor his postings for compliance.
I've written reviews in the past. Like you, I also have a day job and do it for "fun." (Though I sometimes get paid cash money by the publication.) So these rules apply to me, as well. I try to disclose as much as possible any material connections; it is always on my mind for the simple reason that I don't enjoy misleading people. And I think I can probably improve on it, as well.
Ignore this stuff at your peril.
ETA: Also, I'm curious what your policy is regarding the resale of the gear on which you receive a discount. If/when you sell such gear, do you set the price based on retail or the price you paid? In other words, do you try to turn a profit? My personal policy is not to accept more than what I actually paid. However, I guess if it were some sort of collector's item that had an unforeseeable increase in value, I could see reaping the benefit of that.