I shipped my guitar both to and from the UK with zero issues. Actually, customs hit me for fees which I ought not have incurred and I'm still in the process of protesting them (since the guitar was neither bought nor sold during the transit, yet they charged me as if it were). I could've avoided this simply by claiming it had a value of $0, but that seemed to me not to be a good idea. My advice, before shipping via UPS or FedEx, would be to speak with at the very least a supervisor in their customs department, because you will be told different things depending on whom you ask. I didn't ask the right person, and so I shipped the guitar with incorrect paperwork, and incurred unnecessary fees.
Also, it never hurts to be completely honest when asking these questions. I told them my interest was in minimizing customs fees, and they were quite cooperative and helpful.
This discussion seems to be ignoring the fact that hundreds or thousands of parcels go from country to country every day, and at
best what gets inspected in any more than a cursory manner is, likely, a tiny sampling. The only way a brazilian rosewood guitar part shipped - say, from one individual to another, while lacking CITES credentials - is going to receive some sort of rigorous inspection is if there are a bunch of other red flags.
Warmoth ships parts all the time and cannot risk flouting regulations and treaties because the penalty for doing so is severe, the chances of being caught eventually are just about 100% (see
Gibson's factories being raided as an example), and undoubtedly they likely agree with the reasons for the laws' having been created.
I don't really think it's terribly "dishonest" to circumvent these regulations so long as you know the piece of wood you're transporting wasn't, at the time of its being harvested, a part of endangered species poaching. I wonder if a Warmoth employee could comment as to the origin of their exotic wood inventory?