Although there is no way to know for sure what the readers in your area were thinking when they flagged your "pet wanted ad", here are some of the reason why readers MAY be flagging them:
1) no "pets wanted" category
2) millions of unwanted pets to be had throughout country
3) "wanted pet ads" are thought to be lazy
4) soliciting a prohibited item/sale
Finally this quote from an unknown peanut on this subject of "pet wanted ads":
"Pet wanted ads are usually flagged because many readers feel that the space in the comm/pets category should be used for finding homes for existing unwanted pets, they also feel that with millions of unwanted pets there should be no reason on this site to ask for one. If you repost, you may be flagged again."
