Aye Matt,
Change the oil, check all the clearances and pressures and give it a good canter over 100 miles of varied running with a free throttle. When you get back home dump the oil, wash filter and check for "bits or shrapnel" let it all cool down, check clearances again, refill with oil and away you go for another 500 miles, gradually increases the load on the motor.
If it throws a wobbler, send it back to the dealer! Even though the eBay advert says 'No returns accepted'. I think the following from the eBay website applies:
https://pages.ebay.co.uk/safetycentre/rights.html#scratch"Types of statements that are prohibited by law
Any statement which could have the effect of causing the average person to believe that they have less or no consumer rights to pursue a justified claim against a trader is void and may amount to a criminal offence under the Consumer Protection from Unfair Trading Regulations 2008. Below, you will find a list of the typical restrictive statements which may not be used:
No refunds.
No sale goods exchanged or money refunded.
Sold as seen and inspected.
No refunds or exchanges without a receipt.
Time limits for reporting defects e.g. defects not notified within 14 days of receipt cannot be accepted.
If the delivery note is signed then no claims for damages/faulty goods can be made thereafter.
We are not liable for any consequential losses, even if we were made aware of your circumstances.
Notices of this type are not acceptable and cannot be made compliant by including the statement 'your statutory rights are not affected'. Most consumers are not fully aware of their consumer rights therefore this disclaimer is ineffective.
Further information on your rights where you encounter restrictive statements."
As always with eBay "Caveat emptor"!
Good health, Bill