As a Gemmologist let me give you the rundown on a Lab diamond vs a mined/natural diamond. They are essentially the same. I can't tell the difference with a loupe, unless its laser inscribed LG (lab grown) on the girdle and that can't always be seen with a loupe. There is a nice little testing unit that will separate out 97% of natural diamonds from lab. It costs around $1000 and is relatively easy to use.
The other 3% of mined diamonds can only be separated out out at a lab. They use a piece of equipment that costs over $25K and takes someone who knows what they are doing to interpret the results.
Anyone can hand you a report and tell you it goes with that particular diamond. I wouldn't buy one in Africa and expect it to be the mined. Too easy to switch and too hard to prove otherwise for most people. To top it all off mined diamond prices are falling. For a long time DeBeers helped keep prices rising and stable. Now that the majority of mined diamonds are controlled by a Russian firm that is no longer true. Lab diamonds have flooded the market and can be bought for 15-20% of equivalent quality mined diamonds and sometimes even less. Last Christmas and year before my wife asked for and received lab diamonds as part of her gifts. Because of the huge numbers of lab diamonds on the market and the cheap prices it is forcing down the prices of mined diamonds. First time of any significance in the last 100 yrs this has happened.
So use caution buying a mined diamond and don't expect any appreciation in value. Buy a diamond with a lab report and use a microscope to verify that the report number inscribed on the girdle matches that of the report.
Bruce