I’m not sure if the topic belongs to this category. If not, please feel free to move it to the correspong one
As everyone knows, the Forum is full of posts about users seeking advice on whether to cancel orders or not (which would most probably lead to a poor/bad rating) and users suggesting them what to do, disregarding special circumstances surrounding those who seek and normally encouraging into taking the bad review.
For this reason, I thought of writing something that might come in handy when coming across the unpleasant situation of having to decide whether to take a bad review/rating or to cancel and, although it will be useful for everyone, I did it specially thinking in all of us who have low amount of reviews as, when it comes to rating, we are the weakest part of the equation, so I hope you all find it helpful!
I’m not judging goodwilling users for advising others nor it is the purpose of this post  I myself have done it many times or explained the reasons for taking one way or the other. I just think it’s absolutely necessary for all of us to be able to decide for ourselves what’s the most convenient action in a given moment and to achieve this, knowledge is the only possible way, among other things, because knowledge means control. Thereby, having knowledge gives the advantage of being capable of taking action in advance and not at last minute where, perhaps, there would be little to do.
The threads (as there will be at least 3) are not aimed to tell sellers what to do; they are just intended to be an easy and understandable explanation  hopefully  on how to calculate the amount of orders needed to lose and/or to regain points of the most critical rates (Rating & Order Completion Rate).
There won’t be any difficult math associated. At the most, only 3 of the 4 basic arithmetic operations (addition, multiplication and division) will be involved, but please keep in mind that, as I don’t know neither Fiverr’s criteria for rounding up rates nor the amount of decimals used for calculations, numbers that will be given are rough and may vary  but not significantly  depending on each user’s particular case.
Things to be taken into account:

Numbers are based assuming Fiverr rounds up with 0.055

Although combination of ratings can also be made, each quick calculation value was determined taking into consideration only the specific rate as if it were the only one to impact the overall rating.

Except for some cases, values are for losing 0.1 points of rating (whatever the amount) as it bounces down the hill 0.1 steps at a time. These values are shown in tables for convinience and are given as a percentage of the overall amount of reviews (whatever they are).

As referred above, there are exceptions that will be treated distinctively. The reason being that as the minimum of possible orders is 1 (either you have it or you don’t), there are thresholds where, below them, the quick calculation values aren’t applicable due to the fact that rating collapses more steeply on those intervals with just 1 bad/poorly rated order (rating drop > 0.1 points). Beyond those points, the quick calculation values work for any given amount of overall reviews and can be applied directly.
Finding the amount of x * rated orders: How to use the tables

Multiply your overall amount of reviews by the value shown on the respective table on which you’re looking for and divide it by 100. To avoid distortion due to approximation, values are not to be rounded up to the next integer (e.g., 350*0.062 = 21.7 => 21 orders rated 2.5).

The maximum rating value on the tables to apply, will be limited to your actual rating  only orders rated below that value will make you lose points, otherwise, you’ll be gaining them (e.g., For an average rating of 4.7 you can look to values rated up to 4.6 and if the average rating is 3.3, only values rated up to 3.2 will apply).

For those specific thresholds previously mentioned, the determined values will be given within each analyzed case and as nominal rating point loss.
1 * Rating / Review
General quick calculation table
Exception: Interval [1, 27] of overall amount of reviews
For rate = 1, just 1 order will reduce rating points according to the following table:
For 1 < rate < 2, just 1 rated order will make for the loss of 0.1 points of rating according to the following table. Values are the least amount of overall reviews from which it happens. Below them, points will be lost more or less as the above table. For higher values of amount of reviews than the given, please use general quick calculation table.
Note: For 27 lifetime reviews, 1 order rated 1 will drop the rating by 0.1 points.
2 * Rating / Review
General quick calculation table
Exception: Interval [1, 20] of overall amount of reviews
For rate = 2, just 1 order will reduce rating points according to the following table:
For 2 < rate < 3, just 1 rated order will make for the loss of 0.1 points of rating according to the following table. Values are the least amount of overall reviews from which it happens. Below them, points will be lost more or less as the above table. For higher values of amount of reviews than the given, please use general quick calculation table.
Note: For 20 lifetime reviews, 1 order rated 2 will drop the rating by 0.1 points.
3 * Rating / Review
General quick calculation table
Exception: Interval [1, 13] of overall amount of reviews
For rate = 3, just 1 order will reduce rating points according to the following table:
For 3 < rate < 4, just 1 rated order will make for the loss of 0.1 points of rating according to the following table. Values are the least amount of overall reviews from which it happens. Below them, points will be lost more or less as the above table. For higher values of amount of reviews than the given, please use general quick calculation table.
Note: For 13 lifetime reviews, 1 order rated 3 will drop the rating by 0.1 points.
4 * Rating / Review
General quick calculation table
Exception: Interval [1, 6] of overall amount of reviews
For rate = 4, just 1 order will reduce rating points according to the following table:
For 3 < rate < 4, just 1 rated order will make for the loss of 0.1 points of rating according to the following table. Values are the least amount of overall reviews from which it happens. Below them, points will be lost more or less as the above table. For higher values of amount of reviews than the given, please use general quick calculation table.
Note: For 6 lifetime reviews, 1 order rated 4 will drop the rating by 0.1 points.
HAVE FUN !!!
Add: Edited to correct “general quick calculation table” as I wrote it incorrectly.