The standard practice, of course, is for the seller to deliver completed work, and the buyer can then ask for a revision/modification if needed. Most avid forum readers, however, probably know that some sellers and buyers don’t stick to, or even know, “standard practice”, or, rather, the rules.
The above could be a language issue (a problem in its own right but on a differentlevel), however. The question is, did they deliver the completed work and just wanted to remind you to not accept the delivery, if you have modification requests (avid forum readers also know that there are buyers who think they have to accept a delivery, and then suddenly find that the order is completed and that they, in fact, do have modification requests), or did they deliver unfinished work and the “revisions” aren’t modifications/corrections but “buying time” to finish the work?
Depending on the kind of job, several, even many, revisions aren’t necessarily strange, but of course the initial delivery should have been a finished product (that you might or not might wish to be modified).
So, for example, was the delivery a finished drawing of a person wearing a light green shirt, and your revisions are about a different shade of green, or was the delivery an unfinished drawing without colouring (while you ordered coloured drawing and had specified “green shirt”)?
From your account, I can’t deduct whether the seller actually delivered an unfinished order, or just explained themselves clumsily with “first preview”.
In the former case, no, not standard practice nor allowed, in the second case, well, officially, “sellers are not timed on revisions”, although, of course, they usually should be intent on doing revisions as fast as possible for different reasons (happy customer who doesn’t need to wait too long after the deadline, they won’t get paid until the order will be completed, plus 7/14 days, they might expect a bad rating if they take too long, potentiallyan effect on their ranking if they take long with revisions,…).
Personally, if the seller did deliver a finished product and didn’t blatantly disregard my specs, and I want modifications, I’d be patient; if they didn’t deliver a finished product, well, that’s for you to decide.