If paying for a service, I'd want them to do a proper job cleaning the schmoo out of the chain tubes (top tip: tampon on a brake cable) and checking the tracking, both of which are miserable time-consuming jobs that the average LBS, unused to recumbents, is likely to overlook. Tadpole trikes also do a good line in untimely headset wear, so I'd also expect them to check for that. Other than that, it's just the usual bicycle stuff.
The STEPS is pretty much a black box, isn't it? Is there even anything to lubricate?