The first thing I do with a heart necklace is turn it over and look at the back of the pendant. If the back is flat and unfinished, cheap looking metal with no polish, that tells me everything about how the rest of it was made. A heart that's been finished properly on both sides, even though nobody but you will ever see the back of it, is usually a heart that's been made by someone who cared about the bits that matter too.
Length is where most heart necklaces go wrong, and it's not really about taste, it's about collarbones and necklines. A heart sitting right at the hollow of your throat on a short chain reads differently to the same pendant dropped to mid chest, and the wrong one can look like it's apologising for being there. I go shorter under crew necks and higher collars, longer over anything with a plunge or a scoop, because a tiny pendant lost in a sea of jumper looks like an accident rather than a choice. Watch the clasp too. A lot of them are fiddly little springs that are fine for the first fortnight and then start opening themselves on buses, in bed, wherever is least convenient. A lobster clasp with a bit of weight to it is worth the slightly higher price every time.
The difference between a heart necklace that lasts and one that turns your neck green within a month is almost always in what's under the plating. Solid silver or gold, or a thick enough plating over a decent base metal, will hold its shine through showers, sweat and the odd forgotten night with it still on. Thin plating over something cheap looks identical in the shop lighting and then goes patchy and dull within weeks, usually right where the chain sits against your skin. Check the join where the pendant meets the chain as well, that little loop is the weak point, and a soldered one will outlast a pinched one by years. Rose gold and brushed silver finishes hide everyday wear better than high shine gold, which shows every scratch under office lighting. A plain polished heart in a warm gold tone is the easiest one to live with, it goes under winter polo necks and over summer slip dresses without ever looking like the wrong choice for the room.
The mistake to avoid is buying a pendant you love without checking the chain length against your actual necklines at home, in front of a mirror, with the clothes you'll really wear it with. A heart that looked perfect on the shop model can sit in completely the wrong place on you, and no amount of liking the shape will fix that.
