Warning: your travel agent could be stretching the truth about that 'luxurious apartment with all mod cons'. But, if you can't trust brochures, commercial websites or travel agents, who can you trust?

Increasingly, it's real people who real people can rely on: genuine travellers who have been there, done that, and come home with food poisoning to prove it. And it's online where you can find unbiased opinions from altruistic holiday-makers who have written about their experiences just for you. It's called blogging.

A blog (short for web log) is a frequently updated website - the most recent entries (called posts), are at the top, and you can search right through the archive. They range from tedious private diaries explaining what the writer's cat ate for breakfast, to intelligent, entertaining personal musings such as Belle de Jour (the infamous blog of a London call girl, now a bestselling book). And, naturally, some offer travel advice.

There are many sites out there - www.travelblog.com collects posts from different writers as they travel, and organises them by destination. Another good site - www.holidaysuncovered.com - provides tell-it-like-it-is reviews, such as 'the rep never showed her face' or 'the rooms at the Hotel Sol were so damp we came back with bronchitis'.

There is also the option to fire questions at fellow bloggers; often you'll receive a reply within hours. When a friend of mine was considering staying at the Waldorf in New York, he contacted someone via www.holidaysuncovered.com and got the following answer straight back: 'We stayed at the Waldorf and weren't much impressed. There was a flood in our room and the bedrooms were really small.' What these sites offer - and why blogging is proving so hugely popular - is a feeling of trust. And trust is online gold dust.

The word 'blog' is no guarantee, though - advertisers were never going to let that happen. Type 'Cornwall hotel' into www.technorati.com, a search engine that catalogues 13 million blogs, and many of the results are badly disguised ads. Just as with other forms of media, you have to filter out the rubbish. Have you found a blog whose raison d'être is to praise one hotel and area? Stop and ask yourself why that might be…

Unfortunately, that's the flipside of the blogging phenomenon. Private individuals don't have the same incentive to write glowing reviews as hoteliers and tour operators, as one innocent friend recently discovered. She booked a hotel and then, a few days later, idly typed its name into www.tripadvisor.com, a website devoted to 'real reviews from real travellers'. The hotel had awful write-ups, but it was too late to change her booking. When she arrived, however, nervously toting earplugs and disinfectant wipes, she found it just as lovely as she'd first hoped. When she guiltily told the proprietor about the review, he rolled his eyes in that intimate but superior way that is second nature to good hoteliers. 'We have trouble with online reviews,' he said. 'Lots of hotels put up adverts masquerading as reviews. Some of our less scrupulous competitors,' he added, and here his lip twitched with disdain, 'also resort to negative advertising. It is, ahem, disappointing.'
Posting a fake online is much easier than spotting one, and Edward Hasbrouck, author of The Practical Nomad Travel Guides, says: 'If you can't tell, assume it's an advert.' Bogus reviews exploit the naivety that surrounds any new medium.
A long, consistent blog with a single voice (like the excellent www.slowtrav.com or www.newyorkology.com) is much harder to fake than a short review, so it is more likely to be trustworthy. But for this very reason, you know some villain out there will be trying to do it.

So by all means, use the web as a source of information - but take what you read with a blob of suncream and don't read anything as gospel. In the end, of course (and at the risk of flagrant self-promotion) there is one publication you can always trust…