Can I set up some kind of alert to find cheap flights, if I know the destination and dates(with some flexibility on dates)?
And what are the best comparison sites?

Google flight price alert https://support.google.com/flights/answer/6235879?co=GENIE.Platform%3DDesktop&hl=en

Best site for finding flights I find is the map on Skyscanner – you can pop in dates and start airport, and see where is cheap.

https://www.skyscanner.net/inspire/map?preferDirects=true&inboundPlace=BARC&outboundPlace=GLAS&outboundDate=2018-07

I use Skyscanner quite a bit.

For an upcoming multi-flight trip I found Trailfinders on the High Street to be cheaper than any online service (a saving to the tune of £1,200 for a family of four).

Don’t forget because of your cookies, if you look once then go away and come back later the website remembers and put the prices up slightly because it thinks you’re bound to buy this time.

Don’t forget because of your cookies, if you look once then go away and come back later the website remembers and put the prices up slightly because it thinks you’re bound to buy this time.

Yep – after doing your search, clear all the cookies and open the window up again.
My last Easyjet flights kept going up as I was looking and deciding whcih flights to go for. Cleared everything, came back to it and it was back at the original (much lower) price. 🙂

Google flights 9 find the best and quickest. The alert function is great.

Or use two browsers – cookies aren’t shared between browsers.

I just booked flights through Opodo came up with the best price for me.

Yep – after doing your search, clear all the cookies and open the window up again.

Why would/do they use cookies for that?

Sure your IP address could also be used and is harder to fake?

Your IP address can change depending on your ISP’s settings. Also if you are searching from work there may be many computers that to the outside world have the same IP address. Using cookies or webstorage ties things to your computer.

Search on your PC and then buy on your phone/tablet or vice versa.

This is what I do and I have found it rarely makes any difference whatsoever! I’m inclined to think the increasing price thing is an urban myth.

Momondo or Skyscanner

It’s more than cookies. I’ve had it between group of us checking flight prices, all different PCs, IP address and browsers, and the prices were hiking up. Likewise on booking. Best to have one person checking and booking.

Basically prices can go up with perceived demand. Doesn’t always though, and depends on airline.

Comparison sites will have their cut within the price.

Remember, cheapest flight tickets may have catches. No luggage allowance included so have to pay extra, taxes and booking fees extra, restricted seat choices and get stuck by the toilet etc.

On comparison and having to take hold luggage (bike, skis etc), I’ve found overall price can sometimes work out same as a cheap BA flight. More so if the budget flight means going to some far flung airport and thus factor in cost of getting there.