My story is a little different, but in a lot of ways the same, so I will share
I have been with the company from almost the very beginning, before it became what it is today. We used to teach people how to make jewelry and we had to keep an inventory of beads, and findings and all the materials you need to make a necklace by hand. Then they decided it was in everybody's best interest to change the format and become Stella &Dot, which it was in everybody's best interest. But at the time I didn't have a lot of money to go out and buy samples of everything because I still had a lot of beading inventory. They had a contest to earn some jewelry for free, which I won, so I got some free jewels and then I bought what I could afford which wasn't a lot. I have slowly continued to build my display.
So you can definitely start out small and just grow from free jewelry credits and invest some of your party earnings in to the display too. Like Claire said when they see the quality of some of the pieces they have the peace of mind that the rest of the jewelry is of the same quality. I still don't have a huge display, but enough for them to get a good idea.