Image copyrightGetty ImagesFingers are poised and trolleys are primed for the annual pre-Christmas sale extravaganza that is Black Friday and Cyber Monday.Price comparison site Finder.com predicts that British shoppers will spend £7bn in the sales frenzy this year - an average of £220 each.

But bargain hunters need to keep their wits about them - here are some top tips.Be realistic Image copyrightGetty ImagesImage caption The iPhone XS - probably not in the sale You're unlikely to get 50% off the latest iPhone.Newer products are still going to sell well at their original price so there is less incentive for firms to put them on offer - especially tech devices.Consumer website Which also suggests being cautious about apparently amazing offers on unknown brands."Just because a TV has 4K and HDR plastered on the box doesn't mean it's going to have as good a picture as a Best Buy model," the website notes."If you're researching an unfamiliar brand, keep an eye out for fake reviews."Watch out too for unfamiliar stores that significantly undercut their rivals.Trustpilot and Reviews.co.uk are two popular sites where you can draw on past customers' experiences.

In addition, it can be worth double-checking whether the retailer is based outside the EU as that might signal they are selling "grey market" items that the manufacturer's regional division will not fix or replace if something goes wrong.

Sending a camera or phone back overseas for repair could easily wipe out any savings you might make.Bargain checkingImage copyrightGetty ImagesIf you do spot a good deal, bear in mind that some stores change their prices several times a day, so it may not last.In some cases you can guard against this by sticking the product in your shopping cart before double-checking it's a bargain by searching elsewhere.If the store puts the price up in the meantime, you should still be able to complete the deal at the earlier advertised cost.

And if it's gone down, you can empty the basket and then add the product back in again to take advantage of the change.

There are also several websites, apps and browser plug-ins that can aid you on your shopping quest.One of the most famous is camelcamelcamel, which allows you to see a product's historic prices on Amazon and set up alerts to tell you if it drops to a desired price point.Keepa offers a similar service.

You have to log in to use it, but it offers simple ways to check if prices are cheaper on eBay as well as providing an opportunity to bury deeper into the data.Media playback is unsupported on your deviceMedia captionConsumer affairs correspondent Colletta Smith's top tips for online shoppingIf you prefer Argos to the US retail giants, you should try PriceHistory instead.

It lists past prices for items sold by the UK chain rather than drawing you charts, but has a clear user interface and also highlights the biggest reductions of the day by product category.Voucher codes can also help cut prices further.

There's plenty of sites to find them, but you can also speed up the process by adding an extension such as Pouch or PriceBlink, which automatically flag relevant codes for the online store you are currently visiting.

Alternatively, Honey promises to carry out a voucher-scan of its own at checkout and automatically fills in the best code for you if one is available.In addition, you can draw on other people's bargain-spotting skills by checking out HotUKDeals, LatestDeals.co.uk and the MoneySavingExpert forums - all of which offer finds and comments submitted by other members of the public.Stay secureImage copyrightGetty ImagesBeware of email deals that sound too good to be true if you just click that link - and check website addresses very carefully."Making a website look identical to a well-known retail brand is horribly easy," says Prof Alan Woodward from Surrey University."Try not to use a link in an email but rather go to the web address you know."He also advises keeping an eye on your statements in the aftermath of the sales to make sure nobody else has helped themselves to your card details.

Fashion savvy Image copyrightMarlene LeeCelebrity stylist Sulkydoll - aka Donna McCulloch - says beware of a designer garment that is available for half the price if that price tag is still high.

"Think about cost per wear.

If you won't wear it more than 30 times then that 'bargain' could well become the most expensive ornament in your wardrobe," she says.She also suggests checking the washing instructions if you can: "It's not a bargain if you'll spend more than double the cost on dry-cleaning."Ms McCulloch advises caution about the deals shared by bloggers and online influencers on the big day."Don't be drawn in by offers promoted by fashion bloggers about their 'must-have' deals - they may have been paid hundreds or even thousands of pounds to promote an item or brand."Toy storiesImage copyrightGetty ImagesLast week a panel of industry experts called the DreamToys Committee released the products they predict will be the most popular this Christmas - they included Barbie Ultimate Kitchen from Mattel, Lego's Harry Potter Hogwarts Great Hall and Hasbro's Fortnite edition of Monopoly.The group told the TheIndianSubcontinent there will be some deals to be snapped up in the sales ahead of Christmas, but that bargain-hunters should beware of "unscrupulous retailers"."Do your research, look at reviews and make sure you are buying from a trusted toy seller," it said.Remember your rightsImage copyrightGetty ImagesIf you buy anything online you have 14 days to change your mind and get a complete refund, says Sarah Pennells, editor of the consumer finance website Savvy Woman."You may have to pay to return the item, but if the retailer doesn't tell you whether or not you'll have to pay return postage, it's free," she says.Ms Pennells also advises paying on a credit card for purchases worth more than £100 (and less than £30,000) as you are better protected if the firm goes bust or you don't receive your item, than you would be if you paid by debit card.