I sample like CRAZY! I've noted a few different things I've done in past posts...
I've just started to post my sample sizes on Etsy, 2oz mostly. but I always send .5 ounce samples and extra soaps with orders. Not so much for returning orders, but as a thank you to my customers. My samples are always different, and I had a customer e-mail me about how excited she gets when she opens her order and finds new goodies everytime.
If a new customer e-mails me with questions about buying samples, I always send them something for free.
I had a lady e-mail me about wanting to test a pink sugar conditioner, to make sure the smell was what she wanted. I told her I had some half ounce Pink Sugar lotions I had made that morning and I would be more than happy to pop one in the mail for her (for free) so she could smell how good and rich my Pink Sugar blend was. She was thrilled and loved the smell and came back to buy the conditioner AND a full size lotion.
When I sold Mary Kay, forever ago, they taught us A LOT about linking products together to increase sales. By introducing the lotion in a scent I knew she was interested in, I sold a product to her she might not have even thought twice about...
I use to send samples in different scents but stopped doing that. If someone orders a lotion, I send them a shampoo in the same scent...