I’m not sure this is quite right, and while it might just be a question of wording, I think it’s important to separate the “possible / theoretical” side of this stuff from the “actual / likely” side.
The “possible legal implications” kick in the moment you make any unauthorised copy of a piece of copyrighted material - it doesn’t matter how it’s used, how many records you sell, or where it’s synced, if the owner of that material really wanted to come after you, they could.
Of course, we all know that in the vast majority of cases they don’t, either because they never hear the track in question or because they decide not to pursue it. Which links into the OP’s first question - how likely is it that someone’s going to care about your use of unlicensed samples?
This is where the number of records you sell, where the track appears, where it’s synced etc does start to matter, along with the precise nature of the material you’re sampling, how prominent it is in your track, whether you’ve mangled it beyond recognition and so on.
And because the copyright holder could theoretically pursue you regardless of any of those aspects, it all becomes a question of judgment - a balancing act between the creative benefits of using a sample, and the risks you create by doing so. All of which makes it very hard to give any kind of concrete advice, really… each case is going to be unique, so it becomes incredibly difficult to generalise.
I would say, though, that if you look at the general prevalence of sampling throughout underground electronic music, it’s pretty clear that if you were to (for example) include an unlicensed sample in an ambient track that you sell 50 copies of via your personal bandcamp, the odds of license holders noticing, and then devoting the time and energy required to sue you, are going to be extremely low.
Move up to the level of a well-respected artist signed to a bedroom label, shifting 500 copies of a record, a few thousand Spotify streams a month, some press attention & playing a few gigs a year, and the needle moves again. By the time you get to globally successful artists signed to big indies or smaller major label artists (which is where I’d place Bob Sinclair) then absolutely everything will need clearing, no questions.
But that also depends on the material you’re using and how it’s used - a sample of an obscure TV show from the 1970s produced by a company which has since gone bust, spoken by an actor who’s since died, and you’re probably alright, but a leaked training video from the Church of Scientology or some other similarly litigious group would conceivably carry far more risk.
Also, in terms of your other question about how much you could stand to lose, again it all depends on context: are you publishing the music yourself, or via a record label who might have assets more easily linked to the income generated by an uncleared sample? How much money are you (and your label) making from it? Who are the rights holders whose copyright you’ve infringed, and how aggressively are they willing to pursue that?
I’m not a lawyer so I can’t really give you any expert insight on this, but again I’d say that if you’re selling 10 copies of a record, the response you’re likely to face and the financial risk you’re opening yourself up to is going to be very different to if you’re selling 10,000 copies, even if the legal issues inherent in using uncleared material are essentially the same.
