When you attended an auction 10 or so years ago there used to always be a small group of buyers there for the sole purpose of buying a matching set of china cup, saucer and side place - a "Trio". Some of the prices a good trio sold for would have other auction-goers scratching their heads but the buyer would be pleased as punch with their treasure.
And then the prices plunged.....the rise of on-line sites such as Ebay made it easier for buyers to find that rare piece which would otherwise have brought a high price when it appears at a local auction. Recently though, prices have started to rise. With the advent of commercial tea enterprises such as T2 and High Teas being more popular Trios are making a comeback.
Quality makers to keep an eye out for include Shelley, Royal Doulton, Royal Albert, Coalport and Clarice Cliff (if you're lucky). Always check for damage - worn gilt trim, staining which permeates inside & out, hairline cracks and chips. Be aware that with they should always be hand washed as most do not do well with being cleaned in a dishwasher.