Most gigs have 3 “versions”, basic, standard, premium but we only can fill out 1 “gig description” box for the gig, I guess you looked at a gig like that as you say “quite a few options”
(there are gigs with only 1 “Version” too and you can add different things by buying additional “Extras”, but they have been more or less “phased out” and are rarer now).
Those 3 versions themselves, like the gigs with only 1 version, again, don’t always have but can have “Extras” too for additional things, which can make things a little confusing.
The details that differ the basic/standard/premium version of the gig should be in the 3 “small boxes” that describe those “variants”, can be but not necessarily are explained in the 1 “big gig description box” as well (and there are character limits for all boxes, so it can be difficult to put everything everywhere, depending on how much explaining a gig needs).
You may have not checked which “version” of the gig comes with what (vector file) and clicked the wrong “version”, or the seller wasn’t clear in their gig variant descriptions.
if it wasn’t clear from the gig’s set-up in either case, however, and it indeed said it includes the vector file in all versions of the gig but then asked for extra payment for it, you’re right that it was misleading, (purposefully or maybe the seller was clumsy or negligent in setting the gig up (or in editing it in case they included the vector file at one point but later on decided to make an extra of that), in some cases, the language barrier and not an intention to mislead causes that).
I’d only buy from a seller whose pricing and gig set-ups aren’t misleading, there are enough of them, but, of course, make sure to check the gig (and the 3 tiers if there are) thoroughly to make sure you didn’t just miss the relevant info.
I hope that explanation helps a bit, it’s certainly not as if it was a general “Fiverr thing” that prices are misleading, it depends on the sellers if they are or not.
Fiverr itself adds their fee for the buyer (buyers pay $2 per gig / 5% for gigs from $40; sellers pay 20% of their gig price) but I assume you know that from reading the terms and only were referring to “Extras” the seller added to their gig.