Absolutely nothing wrong with buying on Ebay, I bought my BrotherPQ1500s, my Kenmore 158.1914, my White selectronic and my Sweet Sixteen off Ebay- all used machines from private sellers. As long as you are dealing with a highly rated seller, there is not likely to be a problem.
I”ve had situations where a tracking number was given, and the item arrived at my house without ever having the shipping updated. That happens sometimes and have never figured out why. A good seller will not mind receiving a polite, friendly note asking About shipping.
Rob