If buying a used trailer I just factor in new tyres, almost everyone selling will point out the loads of tread on the caravan tyres while overlooking the cracked side walls. Also check the age of the tyres and make sure you have a spare.
If there's no cradle under the 'van just carry it in Bongy and make sure that tyre is good, you'll wish you'd spent the money while you're at the side of the motorway.
I have a trolley jack so can change a caravan wheel but at least your breakdown provider will change it if you have one.
Carry a torque wrench and quality pressure gauge and check both before you tow, only a few seconds and it will pay dividends.
Also check your nose weight is within limits, the lower of the caravan, tow bar or vehicle limits but idealy 5-7% of the actual caravan weight.
Check the You Tube videos and other tips on loading the van to avoid 'Snaking'.
Hope that helps.
