Obviously barring food, I have bought 95% of my and the children's stuff from charity shops, eBay, vintage shops and carboots etc for over a decade. The only things I buy new are underwear and some cleaning products/toiletries (others can be found in charity shops). Sometimes I buy presents new but if I can find stuff that looks new then I'll buy second hand for others too. Loads of people sell unwanted gifts.
But I do it because I love it and because I can buy more unusual things in higher quality and quantity than I can when I buy new. There's nothing altruistic in it (in fact it could be seen as selfish because I am not contributing to the economy when I could afford to do so).
I mainly wear vintage, hippie and handmade clothing so that all has to be second hand. Books, DVDs (and VHS - love eBay for Disney videos!!), toys, music and household items are a fraction of the price second hand and are often nearly new or new. My furniture and appliances are all from eBay, Facebook or furniture/electrical charity shops. As long as you get anything electrical pap tested, I don't see the problem. It means I have a really quirky mix, love each item and consider £50 for an item extortionate!
I'm not poor but living this way allows me to have lots of stuff (I'm a bit materialistic!), fund my children's ridiculously huge extracurricular costs and go to the theatre a lot. We also go (shoestring budget) travelling quite a bit which costs too.