Ahmondjai
If you look up the FAQ of various tent manufacturers , for example from MSR "Do I need to seam seal my tent ? The rainfly and floor are factory seam taped, so seam sealing is not recommended. If any problems develop, seam seal the specific area only" , from Sierra Design : "The rainfly and center floor seam (if applicable) of your tent have been taped at the factory. While seam tape significantly increases the weatherproofness of your tent, additional seam sealing will improve the performance of your tent in rainy conditions." and from Mountain Hardwear " The flysheet is factory seam sealed with hot tape. For most weather conditions, no further seam sealing is necessary. However, if it will be subject to prolonged rainfall or a persistently wet environment, we recommend that you seam seal certain points on the inside of the fly" you get the idea that it is possible (in some cases likely...) that your seam sealed tent will develop leaks (hopefully NOT when new)
Some do that more then others , typically where the tape crosses another seam (cross way) at the corners or the apex.
As a dedicated gear nerd I have spotted several comments about leaks on a certain "top/elite brand" often discussed here too, so this is not confined to cheap brands, just more likely to happen with cheap brands.
So, don't discount tents that you seam seal yourself when new, it isn't a big deal as some make it out to be.
Franco