pitfalls of buying second hand suspension

[IdZer0]

I've been looking at second hand material to upgrade the suspension on my 848 and was wondering what the pitfalls are for buying Ohlins TTX/DU515, possibly some FGRT803/FG511 forks.

I know for the FG511 forks I would need to replace the lower triple, and a new spring (if necessary) would cost around 130€.
I'm worried that they may (or may not) come from a crashed bike or somehow damaged/worn. Are there any tell-tail signs (other than obvious scrapes of course) ? What about servicing I read one guy that already did the service on a TTX and the bill was 300€, is that to be expected if I buy one that hasn't been serviced?