Do any (all?) airlines adjust flight prices based on your past visits / searches on their site?

Not yet.   One day?   Maybe. As things stand today when you look for a seat on a website that website may not actually contact the airline immediately.   Why not?   Well, however robust and scaled the airline systems may be they do have their transaction limits and they will charge if a website makes too many requests compared with the number of bookings actually made.   So what happens is that the websites cache data - if they previously sold a particular flight in the last few hours (or even days) and they've seen plenty of seats available they will store that fact and use it when responding on their website.   Of course, occasionally, they will get it wrong so they will offer you a seat and when they actually go to book it the flight will have filled which is why prices suddenly change during the booking process.   There's another sceanrio as well which happens to people working with the reservations system itself.   Say there is only 1 seat left.   Two agents at the same time ask if there is a seat available on the flight with only one left.   They will both see that one seat.   If they both try to book it then the one whose entries arrives first gets the seat and the other one effectively gets told "tough".   That can also lead to a situation where that last seat has been taken and subsquent requests see no availability but if the agent that took the seat fails to complete the transaction that seat will fall back into availability and the next person to ask will then get the seat.   Oh, and if you wait list for a flight what happens that every so often a program comes across your wait list and looks for availability so if someone cancels a seat at midnight and someone comes along at 0100 and claims that seat and then at 0200 the program looks for your wait list you don't get the seat One last thing.   Some airlines already have "preferred agencies" and those agents may be offered seats at certain fares when other agencies may see zero availability or even not see that booking class at all. So why might it happen? For a start I don't actually see what you're suggesting happening.   On the other hand the airlines (through IATA) have come up with a "wizard wheeze" called "New Distribution Capability" (NDC for short).   Rather than posting lots of links here I'm going to suggest you search for - iata ndc - and I would read the first page of links where you should find descriptions of what it will enable even how it will work (at a high level) and some details of opposition to the proposal. How do I feel about NDC?   I'm not sure yet.   The theory is that they can tailor their offering to you.   So, if their records show you always travel with checked baggage they may show you a fare that includes a checked bag rather than showing you a fare that includes no checked baggage and then you have to look elsewhere for the bag fee.   Or they may see you have occasionally upgraded so even though you've asked for economy they show you an upgrade fare as well.   Those should be positive for us, as travellers.   On the other hand if you only ever travel at THE cheapest fare they may decide you are an unprofitable passenger and decline to offer you a seat.   Of course, this all depends on them knowing who is asking and having records to enable them to tailor in the manner I'm suggesting.   It's also the case that the airlines are pushing the positive aspects of NDC and disavowing the possibility of negative ones.

Absolutely not. I work for BA and this doesnt happen. Ultimately airlines actually work to offer regular customers discounts. Im certainly aware that some discounted upgrade offers are targeted at certain people but this is only after they have a booking made. Usually these are people who are members of British airways executive club who also get other benefits for this. Really there would be no benefit in doing what you are suggesting because even very regular travellers want value for money. The people ive spoken to who will only travel first and business with no regard to costs are few and far between!! It is possible though you are travelling on certain dates or times or purchasing tickets in a way that means you only get access to higher cost tickets. There are stopover, advance purchase and other rules which if you dont adhere to when booking dramatically increase price. My advice is if you think thst might be the case ring and speak to the airline direct. An agent can advise you on fare rules.

I think they do . Recently I had the option of paying a fee and holding a fare in a budge airline site for 24 hours . Almost instantly my fare went up about 10 % when I rechecked it ( although I had it held ) thus giving me the impression I had done well by holding it just in time before it went up . My hold option expired without me making the booking . I them checked the flight again a day later and it had indeed gone up 10 % from my original search Then I did the same search on the same flights on the same website only this time from the ' private search ' option on my search engine . The price was 10 % lower than the original ' held ' price !My conclusion is the more you revisit a particular route / fare they adjust it up and then give you the impression if you don't buy it it will go up even further very soon