Spotted by forum member @Sarin.

Advancement past Sindikat Member does not appear to be possible by buying illegal goods.

"OnGlobalPlayerBoughtItem" in 'unidBlackMarketMember' has a limit in the code, 'maxXP'.

(block (
	(maxXP 1500)
	)
	(switch
		;	If the player bought illegal items from the Black Market then
		;	we add to XP.
					
		(and (objHasAttribute aSellerObj 'blackMarket)
			(itmMatches gItem ([email protected] gType 'smugglingCriteria))
			(ls ([email protected] gType 'xp) maxXP)
			)
...

Advancing to Sindikat Member sets the type property "'xp" to 1500 so this code does not run.
Possibly successful BM missions could generate enough xp to rise to Lieutenant (3000xp) but I can't see how Lord (10000xp) could ever be reached.

derpcat 12 days ago:

I always thought that this was intentional. Did make levelling up very difficult, and I don't think I've ever actually made it to Lieutenant so I never saw if you got anything at those higher ranks.

wolfy 11 days ago:

Interesting catch, looks like it was an intended lock out but the levels/xp gain from other sources was not properly implemented (or maybe the mission chains are incomplete and there are supposed to be future ones that provide more?)
Haven't really done much of the BM stuff so not too familiar with its progression.

george moromisato 3 days ago:

The limit at Sindikat member in intentional: I want to give the player other ways to earn XP. We'll need to add more missions, etc.

See also: https://ministry.kronosaur.com/record.hexm?id=89088