The proof is the product having a Certification Agency's sticker with logo and file number, or that in the owner's manual.
UL Certifications Directory Intertek Product Directories These directories list Brymen, Uni-Trend, Fluke, Mastech, Flir, Keithley, Klein, Keysight etc. multimeter safety certifications giving proof the product was tested and passed.
No sign of any listings for Sanwa Electric Instrument Co. Ltd.
If you want to fake safety approvals for your product, there are many strategies:
1. Use the term "designed to" in all documentation
Meaning the engineers had good intentions but did not test the result to any standard. The expression is a red flag for claims about safety because a design is not a test and you're in a conflict of interest anyhow, this is why third-parties are used.
2. Use old standards
Old, deprecated safety standards are simpler and much easier to meet.
IEC 1010 was from about 1988-1993, when 61010 superceded it.
3. "We have thousands in use and never had a problem"
The number of units sold and hours without incident mean the product is safe. What more proof do you want?
4. Get approvals from a small, unheard of, or inept certification agency
They are happy to take your money and fudge the results, after all they are not liable for testing only as they were instructed to.
As an engineer I have been through the wringer with corrupt CEO's and engineering/product managers, but also a certification agency happy to do the work but not actually qualified for the standard they claimed and pumped out stickers for. We could talk more about NRTL but there are always loopholes people exploit.
My position is the Sanwa multimeters are high quality builds but unknown as far as safety, misleading in their 61010 claims. I'd want to know there are no blatent design/assembly blunders making a clearance violation allowing unexpected arcing, for example.