Hello, Tiger Small Engine,
I used to only buy new engines from small engine warehouse online, but they have gotten out of hand with their pricing. Now, I only use them if the customer insists and has the new engine drop shipped to me prepaid.
Yes, I have sourced and had the customer(s) purchase several engines through Ebay, but I make sure to ask the seller about the maintenance history, hours of use and general questions about it and why the engine was pulled to sell online.
I have purchased 3 used engines for my own equipment so far and have been very satisfied.
The important thing to do on Ebay is ask questions. If they don't want to answer questions or get snippy (red flag), I just move on to the next potential engine for sale. Most sellers are happy to answer questions.
Usually, I find out if the seller is an actual small engine repair person, or just a private (hobby) seller. Once I'm certain of the engine condition, it is up to the broken mower owner to make the purchase. (Yes, I do charge a minor finder's fee for my time.)
I quit financing customers big-ticket parts and repairs years ago.... I have found that customers are more sincere about completing repairs when they have some money tied up in the repair process.
So far, I have had very good results through Ebay. I have had only one used V-twin come in with a failing coil which I considered a very minor problem, and another needed the carburetor cleaned well and reinstalled to correct a poor idle.
I make sure to test run every engine on a small, modified roll around table I have before they are installed.
Used B&S Intek singles are the exception due to their chronic failing cam issues currently happening.
As for transaxles, I try to locate them from a local salvage when I can, or a whole core parts machine on Facebook Marketplace but I will not buy one online (except new). It falls on the customer to take chances like that. The less money I spend on their problems, the better off I am.
I seldom have a customer willing to investing the money to save a machine with bad transaxle anyway, but that may change with the prices climbing higher all the time on new equipment.