In reply to Alan James - Rockfax:
Flight prices are something of a dark art, cookies or no cookies.
A couple of months ago, I was looking for a flight to a US city (let's call it Warholsville) later in the year; it's a regular trip to visit a friend for cycling. I usually fly from Manchester, and expect to pay around 600 quid max. I started looking around July. Shockingly this year, the various usual culprit websites were quoting 900 quid ex Manchester. No cigar on that one. On the spur of the moment, I checked Glasgow (only about an hour further by car in the other direction). Same airline (UA), same gateway city in US (EWR), same timings (Glasgow about 30 mins different from Manchester timings). Answer: 400 quid. Slightly gobsmacked. Checked a few other website to make sure it was bona fide, and didn't hesitate further to book: (very) happy with the deal.
Started daily monitoring thereafter (more out of curiosity, but anorak spreadsheet tendencies don't help!). Flight prices stayed stable, then some very weird price moves early August, then both MAN & GLA stabilised (thus far) at expected 600 quid.
I can only deduce that there was an anomaly in the pricing that someone uncovered and amended, or there was a special offer on somewhere that I didn't see but got to enjoy (I booked via expedia for the Nectar points at same price as going direct - surprisingly).
For the price difference, I could get a gold-plated taxi (I won't, I'll drive); even better, the parking and the Travelodge at Glasgow are significanty cheaper than Manchester
The pricing history graph is at:
https://photos.app.goo.gl/1V1WxgaI2tujSxa13
Apart from silly season around second week in August when prices gyrated until settling down again, the prices have been stable, and I've been checking prices daily using a deep link via Google flight price tracking in same browser which goes direct to airline's own website, so there'd have been plenty of chance to track me, but it seems to have no effect...
I'd say to play them at their own game, be advised, & caveat emptor