They have to ask me if they can use it and for what purpose. And even better, they can’t condition the use of the site/product on me accepting that they sell it.
This is very true. Many sites and services seem to have deliberately misinterpreted the legal text. I hope a high profile target will be taken to court over this, to establish a cautionary precedent. It just hasn’t happened yet.
Every EU country has a data regulator. These regulators have a range of enforcement options at their disposal, from politely asking a company to comply up to a fine of €20m or 4% of global revenues.
You can see a list of previous enforcement action and adjudication decisions by the British Information Commissioner's Office at the link below. These are all under the old Data Protection Directive, which was broadly similar to GDPR but somewhat lacking in teeth. You'll see everything from a slap on the wrist to six-figure fines.
I feel most sites don't comply with the latter half of your statement (conditioning based on acceptance).