Number one mistake is rationalizing that no product certification or approvals are even necessary.One CEO demanded I prove that a product for sale in the USA needed safety approvals "where is it written?". The USA doesn't have Federal law about it, it's the jurisdictions -town/village/municipality that has the laws, as if it's the Wild West. Example NFPA-70 for electrical code, some states
use bits and pieces or do not even require it. Other safety standards are not law until there's a fire or explosion, then the jurisdiction figure it's good to adopt it.
Point is, do your homework to see what the applicable safety standards are or ask an agency for a consult about it- although they don't like telling you that, they are liable for any mistake there.
Number two mistake is getting certification or approvals at the END of a product development project, considered as a formality.Right when the product is "finished" and you're almost ready to sell it, there's this little formality amidst a ton of pressure to start selling it and make money.
But certification will always have findings requiring design changes, unless you've got senior engineers that know the standards and are well experienced.
Some managers try to outsmart the safety standards by coming up with some cockamamie idea, others get furious and hate the certification people (as if they don't notice the disrespect), others find a certification body that is dodgy, there are some out there.
I worked a lot on product development in oil and gas, where combustion, electrical and hazardous location safety standards are to be met.
I've had a CEO, engineering manager push to get it through approvals, regardless if it's actually safe or not. Many noob engineers/techs pleasing the boss and going along with the sneaky moves. One product a mosfet shorted due to ESD leaving a gas solenoid turned on. Well, two explosions occurred and that did nothing to change the ethics at that company. I tell them that product should not even be on the market, I will not sign off on anything about it, and let's shoot that engineer messenger lol.
CE means nothing in North America, china has thoroughly bastardized the CE label with their unsafe exports of mains-powered goods, and fake certificates if any.
I've never heard of the EU actually asking someone to provide CE proof, ever. That they allow this to happen, means nobody is actually doing any policing or enforcement it seems, and china exploits this. Even in Canada there is nothing preventing unsafe china products from being imported, we allow it.