In the end days they will call good evil, and evil good. Most who have never seen a miracle doubt that they even exist, so when Jesus shows up and does one, they are suspicious or even jealous as the Pharasees were, and are.
Remember that those scriptures also speak of those people performing false miracles. It just depends on the "miracle." If it is the old "Make the leg grow" several inches trick (which is a old, and easily duplicatable magic trick), then yes, I would not believe. If I saw a guy buried in the ground in the coffin, that had been dead for three days (like Lazarus), then I would believe.
As much as our Charismaniac brothers would have us believe otherwise, we are COMMANDED to be DISCERNING. We are NOT supposed to believe everything we see. We are warned that the Devil masquerades as an angel of light.
And NO, we are not promised healing in this life. Nor is healing the ends. It is the means. Jesus told us why He healed...
Mat 9:6 But that you may know that the Son of Man has authority on earth to forgive sins"--he then said to the paralytic--"Rise, pick up your bed and go home."
Other times, such as Paul's eyes, and Timothy's stomach, God chose not to heal.
So here it is: if someone healed someone, and then stood up and preached the REAL Gospel (salvation from sin, death to self, repentance unto life, etc), I would say "Hallelujah! Great."
If they "healed" someone, and then made an appeal for money, or somekind of promise of material "blessing" that goes AGAINST scripture (because it does. Scripture promises a Christian will be poor, hated, beaten, and afflicted, and have "trouble in this life"), then I would stand up and call him down for the fake heretic that he is.