For what it is worth in the UK in a lot of high-street opticians they will sometimes try the hard-sell after the exam too. They also recommend that you get it checked every 12 to 24 months as well (at least they suggest that to me).

After the exam ends its somtimes "Let me hand you over to <person> who will take you through the options" and the next thing you know they are trying to make you look at £350 frames, suggesting exotic coatings to the lenses etc.

You're legally entitled to the results of your exam - you are not obliged to buy from them. The exam itself however is usually free so I guess the psychology of it is you feel like you need to get glasses from them since you got the free eye exam from them.

Personally I usually just say "I am in a bit of a rush - I'll come back at the weekend with my partner to help my choose". We both know I'll never do that :-)

There are places where you can order your glasses + lenses online though. Enter prescription and so long as it looks "normal" (i.e. did you enter it right) there are no questions asked. I've had pairs of glasses that have lasted for several years of use that cost £6.99 (no typo: six ninety-nine) including delivery. (from goggles4u if you are wondering - no connection, just a satisfied customer)