Commercials are very carefully researched and very carefully planned, as a rule. The idea behind them is that you are watching TV, and your critical mind is not functioning or at least is not engaged, as the reason you are watching TV is to be entertained, not taught. The critical part of the mind can be disarmed by humor, like the Joe Subaru commercials, or those AXE commercials, where there is this guy on the beach and he is assaulted by several thousand beautiful bikini babes.
The other approach is to subtly hint what buying the product might cause to happen, like the commercial you mentioned. SHe woll bbe incapable of not loving you if you buy her an impressive bauble.
No one thinks that they are ever sold anything by most commercials, but this is just not true.
Oil of Olay had a commercial blitz in the 1980's, and one by one, every product the pushed appeared on my wife's dresser. She had never used it before. When they stopped the ads, the stuff was not replaced. It did not seem to make a difference when I pointed out that one of the main ingredients was monosodium stearate, which is basically beef fat. For all I know, it is beneficial to the complexion, but at the price Oil of Olay charged for it, it was very pricey fat indeed.
Diamonds are graded by letters, something like AAA through M, and the wholesale price varies greatly based on the grade. As a rule, the consumer never knows what grade he has purchased. Size seems to be everything that makes all the bride's friends oooh and aaah.
The justification of buying jewelery-- that is will be worth a lot more someday--is usually bogus, as the markup on such things is huuuge. A friend of mine had an obsession with Rolex watches, and I told him to try a reputable pawnshop. He bought a gold model for $2,100, which is about 2,091.02 less than a person actually needs to spend to know the time of day, but the retail on the model he bought was over double what he paid. You could not tell the watch he bought from new: it came with the box and paper stuff, and he had it checked out and identified as real. Maybe a person who bought a Rolex in 1935 could resell it at a profit today based on the gold content. Of course, 14K gold is not quite 60% gold.
Most often jewelry is stolen or lost before anyone profits from it.