technology costs money, therefore the distribution of technology within the population will follow wealth or income distribution curves. Depending on the gini values for such curves that you decide on your world, the 'commonly used' tech level will probably be far lower than the available tech level, even of locally manufacture goods.
Imports will cost still more and thus be used mostly by those with higher than average incomes. The average person will end up using things manufactured on his own world...aka tech from local industrial/infrastructure capability.
The Earth, taken as a whole, has a pitiful tech level, far lower than the 7 or 8 most people assume, when using the idea that tech level equates to 'commonly used'.
That's why I like so much the Tech Profile in WBH (MT). There, tech is divided in several areas, with the broadest of them being High Common and Low Common. In today's Earth, I guess the 7-8 assumed by most would be the High Common (as is in WBM, the TL listed on UPP is the High Common), while Low common could be as low as 5-6, and even lower in some places and areas (even so, AFAIK there's no place on Earth meriting TL 4, as I guess internal explosion engines and telephones, among other things, are available earthwide).
About offplanets imports, that's represented by the Novelty, and is dependent of the nearest A starport system. There's no equivalent for 21th century (solomani date) Earth.
There was a MT adventure in challenges 48 to 51 (it was given in four parts) that was mostly done in a TL 2 (High Common) planet where the effect of the governement (mostly by foreign agents) having exclusive access to higher TL was well depicted and used:
Behind the Blue Eye.
Its use as an example to this case, though, is limited, as it was represented in Hinterworlds, and most people didin't even know about higher TL, unlike (or so I understand), most Imperial worlds, where most people knows this tech exists, even if they have no access to it.