Another advantage of buttering up an engineer through selling to them is it saves mats, which for a new player can be significant. The higher your access level, the less mats it takes to complete the rolls for each grade. For example at G5 access, a G1 mod always takes a single roll. But if you attempt a G1 modification at the lowest access level, a G1 mod can take four or five rolls. So by increasing rep before applying the modification, a player can save quite a few mats through the grades.
It had been some time since I tried to unlock an engineer. However I'm in Colonia to unlock the engineers there and I did lightweight heat sink at Petra. Starting from zero, it took four rolls and four phosphorous to complete G1. Each grade above that also took more rolls than usual. Now that she's G5 access though, it's back to the most efficient.
So buttering up an engineer through exploration data or commodity sales can save mats as well as allow a player to pin higher level blueprints than his or her current mat stocks allow, saving trips back to the engineer and allowing remote engineering at the highest grade.