To be honest, your problem here might be communication and/or simply asking too much. For example, I see lots of ‘I will remove the background from your images’ gigs on Fiverr priced at a very reasonable $5. However, your ‘cleaning about 100 images from the background’ just sounds confusing. Also, I would guess that you would be looking to pay a reasonable amount for this? - It doesn’t really strike me as a $5 job you see.
Anyway, communication is vitally important when making an order. This is because as well as it being important to give your seller a clear a brief, quite a few buyers are purposefully vague when contacting sellers to ask if they can complete a certain task.
For example, I get messages almost every day asking how much for x amount of articles. At first, I used to find this confusing as my gigs are very clear in regard to my pricing. In this case, I would quote a price of $5 per piece only then for an order to follow for something like 5 x 1000 word articles about a specific forex trading niche, each of which would need to be written according to a set of detailed instructions. (Something I would usually charge at least $20 per piece for).
In this case, I now ask such clients to tell me what they want an article written about and what kind of word length they are looking for prior to ordering. - And I usually don’t hear from them again.
However, there is also a second type of buyer, one who will order something for $5 directly, only to then say that for this 1 order, they actually need 4 x articles or articles + images & uploading to wordpress etc. In short, they think that making an order entitles them to whatever they feel like is a reasonable amount of work.
Now with any order like either of the above, I simply request cancellation. Also, because some days I can’t realistically check every order that comes in, I might not request a cancellation for 2-3 days after an order is placed. The result of this is a furious buyer or two.
My guess, in this case, is that if you are placing orders or requesting work as vaguely as your ‘cleaning about 100 images from the background’ sounds, you are quite possibly setting a few sellers mental scammer alarm bells ringing. - You certainly would mine and this might be why your orders are being cancelled.
In this case, you can perhaps try to avoid disappointment by contacting all sellers in advance in order to ask them how much they would need to complete your task. In the same message, you should describe your task as clearly as possible and upload any reference materials. If you are made an offer by a seller, you might then think about checking in with them as your order deadline approaches in order to check that everything is okay.
Also, you should always keep in mind that what you consider ‘easy’ might not be the same as a task actually being easy. Don’t assume that someone will be willing to cut a few images out of a larger image just because it is easy to do. You also need to keep in mind how much time a seller will realistically have to spend on a task and that if they usually charge $5 for removing one image, they will likely want a bit more for removing 100.