Is it legal to withdraw an advert for a rental property and resubmit at a higher price?

You are not comparing Quality street with Roses there...😀 increasing the price of a rental property just like you can with FMCG is not the same comparison and may be illegal if the propery is in a rent cap area and is subject to rent cap

Op, is there a rent cap in place ? Is the ad for a room in an apartment or a full let of an apartment?

how is it unethical?

No , but if I had a spare gaf and I legally stuck it up for 1500 quid , saw jaysis that some serious interest why not stick it up for more, once abiding by your rent cap. Is renting for a profit unethical?

Assuming that they are not breaking a rent cap then I can’t see how it would be illegal or unethical! In fact imo they would be insane not to get the maximum rent possible given that they will be wedded to it for ever more. €100 per month over years will very quickly add up!

if it’s in an RPZ zone - then there could be an issue, unless it’s first rent, or a clerical error. Either way, best accept or move on

The price of a rental will be decided by the market factors. There is certainly a lot about the housing market that is unethical and sickening in the extreme, but the property owner may list his/her property for whatever price they want. It would only become unethical if they were to offer it to you at a said price and then put it up after an agreement was made.

There are ways of using google / wayback that can bring this stuff to light. I think it is very scummy to raise rents above the RPZ rates (even though I really dislike the RPZ process, I believe in playing by the rules, or changing the rules)… and it really seems like there is some evidence that this is happening here. The other clue is 'filthy apartment'.