I don't get it. If you go to a parlour where someone speaks little or no English, how can you do the most basic due diligence of asking whether they're there willingly? Spelling it out - if you have sex with someone who has been trafficked, coerced and possibly threatened with who knows what, there's not much difference between that and rape.
The language competency, lack thereof, is part of it. Employers are only granted employment permits for overseas applicants if no British resident is capable of doing or available to do a given job, and the job must either pay a certain rate; or have an exemption. Examples which apply to males might be taxi-drivers, halal butchers, or 'chefs', where knowledge of and expertise in certain cuisine might be deemed essential. Back to the sex-trade, nail-bars, massage venues, restaurants and garment manufacturers provide the necessary cover for the required 'expertise', and this is helped by the interchangeability of the applicants and language barriers - for example if someone only speaks (or pretends to) with a dialect that's not straightforward to translate, the process of establishing if they're legitimate workers is prone to delay and obfuscation.
So, we have to ask ourselves, what's the likelihood that, say, a waitress, a nail bar or beauty-parlour assistant, who has no fluency in English, is really here because they're an essential worker and earning above £25k - and if the answer is 'not-likely', and the venue, whatever it is, is associated with nations known to be knee-deep in trafficking, then there's a better chance that we, as patrons, are abetting that which we claim to abhor.
any nationality can be coerced/trafficked
There's an exponentially higher risk and occurrence in/from poorer nations.
True, but I believe that traffiking/coercion is much more prevalent among Chinese girls than other ethnic groups.
Obviously, I look for signs of coercion in any SP.
We really can put most East-Asian nations in this at-risk category; with exceptions for Japan and South Korea.