Your assumption is wrong.
First of all, there's a big difference between a CONDO fee and an HOA fee. A condo could have both, or it could simply have a condo fee. So if you're seeing condos with no HOA fees, it could simply be because there is no HOA fee.
Second, depending on the MLS, it may be easier or more difficult to list a condo fee or an HOA fee. Some make it very difficult, so you'll see the fee put in under "utilities," for instance. Sometimes it'll be mentioned in the "Comments" section. It's not necessarily a deliberate decision by the agent or owner to hide anything.
How can a buyer tell if the fees are going to increase? Generally, that's pretty simple. Look at the HOA's financials from the past 3 years. See what the pattern has been. See if the fees are covering the expenses. See if sufficient money is going into any needed reserve funds. (That more often comes up with condo fees, with reserve funds for building boilers, roofs, elevators, etc.) And watch for this trick: Some associations keep their fees relatively low or stable, but every year do a special assessment. You need to know whether, and how often, special assessments ahve been done.
How can a buyer tell if there are caps? Usually, there aren't any. But it's very simple to tell: Read the condo or HOA documents and see if it addresses caps. If not, then there are no caps.
As for the amount of the condo fee or HOA, you also have to take into consideration what it's covering. Swimming pool? Club house? Tennis courts? A security gate with guard? Common area maintenance. And so on.
Hope that helps.
Sometimes, it's simply a matter of omission, or mistake on the part of the listing agent.
For the most part, realtors know which condo complexes will have high HOA fees due to the number of amenities and the age of the property. So even if this info isn't on the MLS, many of us will have an idea, and have a way to find out.
Until one sees the CCRs, articles, and other HOA documents, one can't know how often or high the HOA can be raised.