This is a long answer but it's not a simple subject.
You have mentioned the Lacey Act a couple of times. I have not hunted in Africa yet, but I have a pretty good amount of experience representing clients charged in Alaska with Lacey Act violations. It's nothing to mess around with.
There are many aspects to the Lacey Act but the one I see most commonly is people who violate local fish and game laws and then ship an item in interstate or foreign commerce. If the value of an item is >$350, it's a felony. So in my neck of the woods, someone shoots a bear illegally and ships the bear hide back home, if the value of the bear hide is >$350, it's a felony. How do they determine it's >$350? Because Alaska wildlife troopers auction off seized horns and hides, including DLP (defense of life and property horns and hides, every year. And bear hides routinely go for more than $350.
Alaska game laws are complex. There are 26 game management units and those are broken down into further sub-units. The laws, including seasons, legality of animals, and methods of taking them vary from sub unit to sub unit and sometimes even within a sub unit. Generally, I don't see naive clients get charged. That is, if an unscrupulous guide dupes a client, the client is not likely to get charged. BUT ... federal fish and wildlife agents will visit the client, the client will have to give up any trophies that were obtained in violation of state law, and client might be a witness against a guide. Usually, though, clients know.
As one example, I represented a client who was charged with conspiracy to violate the Lacey Act. She and her son had an interior brown bear hunt. Flew out with the guide on August 9. Season started August 10. Alaska has strict laws against hunting the same day you are airborne in a charter flight, i.e., flying from Anchorage to Bethel aboard Alaska Air does not prohibit you from hunting that day but hopping on a bush plan to land at your campsite will prohibit you from hunting that day. These two hunters flew from Fairbanks early on August 9 and set up camp. While setting up camp, they see a really nice brown bear. Guide says, "We may not get another chance like this again." So they go after it. Son shoots it and she signs a statement that the bear was taken on August 10. Bear hide is shipped to their home outside Alaska. One of the guide's employees tells the feds. Can't remember if he was under investigation or if he just went to them. Tipped them onto this guide. They did a big investigation. Guide cops to a lot of violations and brings up this client. Client gets charged because bear was taken out of season and after same day flying. We resolved it for a misdemeanor because she was not the one who pulled the trigger but as part of her agreement, she could not hunt in the US for 5 years but she was able to keep her gun rights.
So, what can you learn from this?
1. In my experience, clients frequently know when they are breaking the law. In the example given by OP, the client went from one country to another. That should have been a huge red flag even if the client knew nothing else.
2. Clients have an independent responsibility to familiarize themselves with the game laws of where they are going. Alaska's laws, for example, are easily accessible online. I would anticipate one could likewise find the applicable laws for the countries where one is going to hunt. One aspect of pre-hunt preparation should be reviewing the game laws.
3. This guide had a good reputation prior to this event but he was willing to bend the laws when the opportunity presented itself. The investigation showed this was not the first time or the only time. So if you are a client, you should do your due diligence in hiring a reputable guide but also recognize that even PHs and guides with good reputations might recommend doing something illegal. Due diligence would mean: ensuring the PH is properly licensed; checking references; seeing if the PH is in reputable professional organizations, such as SCI.
4. One thing I've learned in this business is that in the right circumstances, anyone is capable of anything. And if you've scrimped and saved for years for your dream hunting trip to Africa and you see a kudu of a lifetime but you can't shoot it, don't blithely say you wouldn't pull the trigger. Say you hope you wouldn't and pray you aren't put in that situation.
5. If, God forbid, you do something stupid and 6 months later or 2 years later federal fish and wildlife agents show up on your door, SHUT YOUR MOUTH. DO NOT TALK WITH THEM. Get their contact information, such as their card, and get an attorney IMMEDIATELY. Get an attorney that has experience with federal criminal charges and with Lacey Act cases in particular and have your attorney reach out to the agents.
Lastly, irrespective of any legal advice, I'll say it isn't worth it. Not just for the risk of prosecution, which is real, but also for the trophy. Every time you see that trophy, you will know you cheated and that greatly diminishes the enjoyment of any illegally gained trophy.