Not sure Trading Standards is the answer, I cannot see any breach of selling regulations.
I'm not actually duplicating what you are seeing. If I put Beta Sitosterol into Search 233 items appear , and all different prices from different sellers.
Granted, there are several priced at around the £17.13 mark, is this what you are seeing ? Many of those are the same, or a penny or two different in price, this is perfectly normal for sellers to try and out price even by a penny, their competitors as they know many buyers search and buy using ' lowest price' in Best Match.
@martyhoyda-2