We gave five treasure hunters €100 each and sent them off to bag bargains. At the end of the series, James O'Halloran of Adam's Auctioneers will value the items and the winner will get €500 for the charity of his or her choice. Rosita Boland's chosen charity is the Sick and Indigent Roomkeeper's Society, Dublin's oldest charity.

Car-boot sales, charity shops, yard sales, flea markets, local markets: I love them all. I’ve been hunting and trawling through these places all my adult life. It’s not only that, like most people, I love a bargain. It’s more that I really love unusual things, whether items that represent social history, such as vintage magazines, pieces of crockery, furniture, jewellery and clothing, or bric-a-brac that you can’t buy new because it is not made any more. I am fascinated by the flotsam and jetsam of once-everyday life that has now drifted far out to sea, eventually washing up on the ad-hoc shore of some second-hand sale.

Mostly my purchases are modest in size and value, bought simply because I like them. Vintage, mismatching china and glasses. Costume jewellery. Books. Magazines. Small, beautiful boxes. An original Anglepoise that cost me £5 and lasted 12 years as a bedside lamp until it finally conked out in April. A 1960s radio that is still working. The mirror that cost £10 in a charity shop 15 years ago and still hangs over my living-room fireplace. The biggest and also the most expensive piece I ever bought was a 1930s cocktail cabinet with a glorious mirrored interior for €100 at the Blackrock Market.

I try to use everything I buy: the vintage glasses and crockery get used in rotation; the magazines and books get read; the cocktail cabinet regularly performs its mirrored Open Sesame; and the pair of 1770 silver salt cellars I bought for £3 in a charity shop in Surrey are on my table, continuing to dispense salt as they have been doing for centuries.

So being given €100 and a challenge to go off and buy something second-hand to be valued by an auctioneer is pretty exciting. I arrive at Fethard’s weekly car-boot sale, which has been running for 30 years now in Co Tipperary. I have been to this sale before. I have come away with six Japanese hand-painted plates, a wooden box, Limoges china coffee cups, and sundry other lovely things for a handful of coins. But now I have €100 to spend.

At this point, I start to mildly panic. It’s one thing going happily and mindlessly trawling through flea markets and charity shops looking for things on your own behalf, but quite another when you have the responsibility of trying to raise money for a deserving cause.

Old shipping containers

Fethard car-boot sale – entrance costs €1.50 – is partially conducted out of old shipping containers, partially under what seems to be an old shed or barn, and partially at outdoor stalls. I am banking on buying something from the woman who runs her stall out of a container close to the entrance, whom I remember having beautiful things for sale. Within five minutes of walking in, I realise she isn’t there. She is, other stall-keepers tell me, at a festival.

My game plan is gone right away. My mild panic shifts up a notch. I search through boxes of €1 worn shoes, boxes of countless copies of Fifty Shades of Grey, and others that contain door handles, apple peelers, nails, cups, saucers, grapefruit dishes and plastic toys. I examine an ice-cream maker in its box for €10. There is even a car for sale at the car-boot sale: a 2004 Opel Signum for €1,600. I have a moment of simultaneous nostalgia and relief when I see a manual typewriter for €35; nostalgia for the person I was when I pounded out two books on a similar machine, and relief that I never have to do that pounding again.

I have still bought nothing, and I have not even seen anything I think will make an auction item. With my own money, I buy a €5 box of Wexford strawberries as a gift. I buy a cotton Japanese handkerchief with a pastoral scene on it for €1, still in its box. I take it out of the box and wipe my hot, panicked brow with it. I buy a little 1950s bowl with a sailing boat on it for €1. I buy a set of old brass fire irons for €8.

A kind man will not accept any money for a stack of 1960s Women's Weekly magazines that he says came from his shed. I laugh my head off at the stall selling six duck eggs for €3, that has a sticker on the egg boxes with a picture of a yellow plastic duck looking at a real yellow duckling, and saying: "I got plastic surgery done." The two €50 notes designated for the auction purchase are still folded tight in my wallet.

Then I find Tom Lawlor's stall. He has been coming to the market for 30 years. A tin-plate red train engine on display under glass catches my eye. I know nothing about tin-plate toys or trains, but it might be promising, I think. I am shocked when he tells me he is looking for €70 for the Chad Valley Prince 6220 engine. "It's very rare," he says. Is it worth it, I wonder. I covertly do a Google search on my phone, but come up with nothing, other than the fact Chad Valley is now part of Argos.

I tell him I will think about it, and go to check for the fourth time that the lady with the beautiful things really isn’t there, and keep searching. At the back of the market, among fishing rods and mirrors and clocks, I see a wooden chest.

It is hand-carved and looks old. Or oldish, at least. The carvings, of figures and geometric shapes are simple and arresting. I don’t recognise the patterns, and nor do I know what kind of wood it is, but it is lovely. The stallholder says it came from a house clearance in Broadford, Co Clare, from what appeared to be a military house. He is asking for €25. I bargain him down to €20 of my own money. I will use it for my vintage magazine overflow, I think. Because it is so cheap, I don’t think it is auction material. Or is it that I don’t trust my own instincts?

My plan for the auction item is to return to Tom Lawlor’s stall and do more googling before I start to bargain. But when I return he is packing up, and my panic levels ratchet up to 10. Within five minutes, I have bought the engine, two non-matching Chad Valley carriages, and a section of track for €90. Have I made the right decision? Our valuation adjudicator, James O’Halloran, will be able to tell.

Next week: Simon O’Connor of the Little Museum of Dublin bags a bike