Houses, boats, medical equipment & building equipment.
Well i'm not sure if this qualifies as a high profit margin, but have you ever considered selling clothing? High end clothing goes for a lot on ebay. I mainly sell men's shirts that i get from thrift stores, garage sales and etc. I'm able to get them for around $4 and sell them between $15 and $40 depending on the brand.
I have a blog related to selling on ebay here: sellonebayforprofit
Last time I heard it was 18 year olds selling their virginity....
Please do not promote yourselfThanksss