I was shocked when trying to book Eurotunnel in November that every time I looked the price had gone up significantly.
I swore a lot and declared that they could poke it - I wasn't up for all those kind of internet shenanigans.
My husband, sitting in the office behind me and a frequent business traveller, once he stopped laughing at my complete naivity, took over the booking and, having found the best price options, cleared his computer cache and - hey presto - much, much cheaper prices appeared.
I think this is very sharp practice and can't believe it's legal!
In the end we booked two 'there-and-back-in-a-day' tickets and only used one part of each, giving us a lovely 2 night stay in France for a very modest amount of money. I think we paid about £130 for the four crossings, two of which we didn't use. This seems wrong to me, since presumably people are then turned away from trying to book if the train is fully booked because we have two crossings booked we never intended to use.
Ridiculous that you have to be 'in the know' to achieve an affordable crossing. It's worse than trying to buy a rail ticket. I really do not approve, but if I boycotted I would've missed out on my lovely little French sojourn.