What does Schindler promise potential Jewish investors in rereturnf for their investment

He offered them a chance to work in his factory and escape the nazi camps.

In the movie, he offered to unofficially give his jewish investors some of the goods, cookware, pots and such, that his factory was producing. This was a good deal for them because they could easily sell or trade these things on the black market, but the German goverrnment would have taken any offical proffits that they might have otherwise made.

In real life, the "Museum in Schindler's Factory in Krakow" (1) tells us that Abraham Bankier and Samuel Wiener, were two members of a group of Jewish business men that had previously owned and financed the factory that was later confiscated by Schindler, and that they financed him. A quick google of the names tells us that (2) Abraham Bankier was "hired" by Schindler to help manage the company for him. He was also a black marketeer and worked tirelessly to bring more of his people to work at Schindler's factory in order to protect them and save their lives. He was later personally rescued by Schindler from a train headed to an extermination camp. He had been seized along with several other workers because they had forgotten to go to the Jewish Labour office to obtain their new work permits. (3) He ended up surviving the Holocaust and lived another 11 years.

Very little, if anything, can be found online about Samuel Wiener.

1 http://www.krakow-info.com/schindler4mobile.htm

2 https://www.revolvy.com/page/Abraham-Bankier

3 http://www.holocaustresearchproject.org/survivor/schindler.html