A massive name, a faker's favourite. To prove it would transform the fortunes of its owner Patrick Rice, who has devoted a large part of his waking hours in retirement to prove it.

Authenticating paintings is engrossing but fraught with dangers.

The auction world is relatively unregulated and stepping past the landmines a collector's necessity. But there are simple starting points for telling a dodgy picture from the real thing.

So here are my five tips for when you're buying at auction. The same tools can be used in the buying process from antique dealers or gallery owners from whom it is often easier to get clear, protective guarantees.

Cheese in the trap

Question what you see. Pictures for sale can be signed by big names like Picasso or Turner or with exciting looking labels on the reverse indicating exhibitions or collections.

Be deeply cynical.

Have a look at the cataloguing. If the auctioneers have not made any reference to the obvious artist they normally know something you don't.

I call these Cheese in the Trappers (Trappers for short). They are extremely common, particularly in less well-known auction houses or on internet sites, and often estimated at under £100 to lure the unwary.

Framed by the frame

A frame can be an excellent way of outing a fake. Most fakes or trappers at sale are done in the last year and the frames are modern or wrong.

Most serious 20th Century artists made sure their pictures were properly framed, or at least their dealers did.

Wrong frames look too modern, or cheap, or cut-down from something bigger. Often they don't quite fit, like hand-me down trousers.

Bendor Grosvenor, Fiona Bruce and Philip Mould in Fake Or Fortune?

Health check

A knackered picture is relatively worthless. Many people are taken by paintings that may be old and possibly by good artists but that have been so over-cleaned or butchered by amateur restorers that no one wants them.

When an old painting has been savagely over-cleaned or overly-pressed onto a fresh canvas (called re-lining - a common process of restoring old oil paintings) the surface details are often lost.

Done more brutally still and the whole top layers go, leaving no more than the preparation layer.

At this level you can often see the gauze of the canvas beneath. Remove that and you have no more than the bare bones - ie raw canvas!

The usual way of dealing with wounds like this is literally to repaint those areas. It's called overpaint or inpainting. Whenever this in evidence it's a big warning sign.

So look out for raw canvas and overpaint, also later daubing that covers damage like a badly touched-up car chassis.

Another way of spotting overpaint is that it often covers over the craquelure - natural cracking found in old paint - in a way that looks stodgy and clumsy.

Plumbing the past provenance is often key.

Try to ascertain recent ownership. Trappers or fakes normally come from 'a little old lady' a 'house clearance' or 'we just don't know'.

Use your instincts here. Bluff has a way of sounding hollow or evasive.

Trust your eye

Get to see as much real art as possible and don't make too many apologies for the potential purchase in question.

Countless times I have been shown pictures that purport to be by a great hand on 'a bad day'. In my experience good artists don't have bad hair days - just the odd lazy or distracted moment, and the coiffeur remains detectable.

Philip Mould is an art expert and the co-presenter of Fake Or Fortune?.

Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.