The way to check if the sump pump is dying, or if there is a problem of some kind, is to find the model number, and then find how many gallons per minute it should be pumping, and then measure the discharge by seeing how long it takes to fill a 5 gallon bucket.
It really is a simple procedure to replace a sump pump. You will probably be able to buy and install a pump for 1/4 to 1/3 of what it will cost if you call a pro to furnish and replace the pump. If capacity is marginal, larger capacity pumps don't cost a lot more.
There are other things you can check, such as whether there is junk in the pump, or whether the discharge is restricted. Where does the pump discharge go? To get maximum capacity, it should have a large discharge pipe and discharge as low as possible.
The lowest point is often a sewer in the basement (usually illegal) or dump it out on the ground. The best legal outlet is probably out the lowest window convenient to the pump, and the pipe should be pulled down to ground level with something done to hold it there. The siphon effect from a low discharge after it goes out the window actually increases the discharge rate. It should discharge far enough away that it will drain away from the house.
If you can find the make/model, post it here and you will get a reply on the expected capacity of the pump. Many submersible pumps can be used as replacements for pedestal pumps, and you will probably get more capacity at lower cost. You basically connect the discharge pipe, drop them in the "sump", plug it into a convenient outlet, and let it pump the sump out.