What bike are you going to buy?
The first service for most bikes does not usually entail a valve clearance check as it's only 620 miles.
So it's oil and filter and any checks/adjustments the factory bulletins advise dealer shops to perform. Easy to do the oil and filter but you can't possibly know if there is a software patch or an inspection required on the batch your bike came from etc....... and it isn't a huge amount of $... often it's a paid in the deal 'free' service.
You can save that with the inbetween oil changes before the next official warranty service. If anything goes wrong in the first year you will want to have your warranty in order.
Valves aren't usually looked at until 30,000kms/19,000miles (on the SDR/GT models)...... I used to do my own shim adjustments way back in the 80's on my Kawasaki's but I did have some basic training from a Kawasaki mechanic), but after helping my cousin in his bike service shop in the 90's-2005, I realized pulling camshafts out to swap/change shims under buckets on 4cyl engines wasn't my strength. In any case, my clearances didn't change enough to need adjustment with regular oil changes so it's not really an issue until 19k miles (30k kms) if you have an SDR/GT.
If you have a 690...... the dealership may be wanting to check or replace your cam followers as there have been a number of failures in certain model years.
There has also been a couple of posts about camshaft oil jets becoming blocked. I haven't read why this happened, but I have read a recent post where an SDGT had surprise cam & follower wear that was noticed by a non KTM service shop which referred the owner back to a KTM dealer to be inspected and luckily accepted as a 'goodwill' warranty repair - so the dealers aren't always the enemy
..... even though we all have tales of errors/shoddy work to tell.
I still consider the 620mile/1000km service a worthwhile thing to have done on a new bike/model - unless you are a long way away from a dealer and maybe have their agreement to just do an oil & filter change on your particular bike (they should know if it really needs to come in for special treatment or not).