Most common mistake is not adhering to the specified time, usually waiting at least 5 min for the glue to dry and less than 10 min. For cleaning lighter fluid is good or paint thinner. Too much glue can hurt but in practice it needs to be way too much to hurt. Not spreading glue widely enough can hurt. Another mistake is in rushing and crumpling the patch. To be honest, good patch kit is better than cheap, but cheap should work well enough for most situations. Certainly the outcomes you are getting sound like operator errors. I buy Rema patches, kits and/or glue, because overall the contribution of materials is marginal compared to the time and work expended putting the patch and dealing with one that does not hold. There are no savings to speak of buying cheap stuff but, repeating, on a case by case basis the cheap should work.