I disagree with @humanissocial on this one. Even with services your can have sales to improve conversions. I sometimes do a sale on my services outside of Fiverr, by simply adding a 20% discount on for example audiobook recordings in the summer, when there’s usually not so many bookrecordings coming my way. That has improved my audiobook recording sales in the summer by about 30%.
You can absolutely offer discounted prices to boost your performance, even when offering services and not static products.
But, as of yet, there’s no such function here on Fiverr. What you could do is include in your product description that you offer discounts for certain services (I offer discounts on orders of 2000+ words), but I don’t market that as a “sale”, and I’m unsure if that would be ok for Fiverr, since it could give the impression that Fiverr is offering discounts and not the seller.
So I wouldn’t do that without first asking the support team if it’s ok to actually market a sale in your gig description and/or gig image.