We have the same rule in our local RC forum, one bump/week. It is very reasonable because you gain nothing by bumping daily (or you might even irritate the daily readers), to be honest I was quite surprised to see here no limit bumping allowed.

In our sales forum nobody is counting the days and we discuss freely (and add pictures) like here but when somebody is abusing the terms it is quite clear.

We have one more rule.

You can bump anytime if you drop the price significantly (like 15-25%).