Spending huge $ getting a product certified to any standard does not keep lawyers off your doorstop. Anyone is free at any time to sue you for absolutely anything!
This is a good point. You can't fully protect yourself against any such thing.
And - like the others here say - it doesn't matter.
I'd just like to point out one side of *why* it doesn't matter.
I'm still fairly young (30-something), but in my experience with business and regulatory matters, most people are actually not evil twats looking to burn you. They're just not. And why would they be? Hurting you rarely gains them anything, and it's not how most people wants to be, or be seen.
Empirical evidence time...
I had an encounter with the radio-regulatory people in a country once, due to interference from a device we'd sent a customer (but not made). The device was actually within spec, but caused some issue for a receiver, and the device had actually been hunted down because of this. Everyone went "Uh, oh!", but I just pulled out an old receiver, reproduced the problem locally, sent graphs back to him. He seemed happy because he'd met someone on our end that cared about the problem, grabbed hold of it, and spoke the same language (radio) as him while looking for a fix. We found a more suitable device, dropped of the device and some frequency graphs with them, and by the end of the week, everyone was happy. Especially me, that got an open invitation to drop by the techs home for a cup of coffee, and finally get my paperwork done to get certified HAM-operator.
Lesson of the thing? They weren't "out to get us", but they cared about getting the issue resolved. Meeting someone that also cared, made them relax, and it turned into more of a cooperation thing than opposing fronts.
Back to DIY-kits, there's generally three concerns people seem have:
* General safety of the kit
* EMI-issues
* Business-aspects, patents and the like
For all three of those topics, the same really does apply. Do your best and - if there are issues - take them seriously, and cooperatively work things out.
If someone points out a safety-hazard with your product, that you hadn't thought of, I'd be willing to bet good money that most DIY kit-makers would listen attentively and see if they issue could be resolved or improved. No conflict as far as I can see. Nobody wants dead users.
EMI-issues? Take them seriously if you get a request, try to keep an eye on good design, and if you can, check out frequencies you worry about, especially on high power rails and the like.
Business-wise? Sure, if you try to make an exact copy of a product, you might get issues, but that's not typically what you're doing. It's unlikely, but if some lawyer sends you an angry letter, don't reply back in the same tone, but don't fall over with fear either. Just reply back asking if they could explain what their concern is, to see if things can be worked out.
Inventing some numbers, it wouldn't surprise me if 99% of small kit-makers never get any trouble, and if 99% of those that do can be worked out fairly easily.
tld