Is there any sort of tester you can use to test for signal strength on RJ45 wall outlets?
Yes, but they cost. Generally, unless you are running high grade networks (10gb+ or 1gb+ over longer distances) a simple continuity tester (like the one MrSaffron linked too) will tell you of any glaring faults with the cabling (in my experience it is almost always a termination fault, but cable faults do happen)
I'm having some latency issues i.e. takes ages getting ip. I was wondering if it's to do with how my electrician laid my cables and sink in the surface mount box? I let him lay the cables because he's supposedly good at it. I made the connection to the wall outlets.
If you get delays during the initial negotiation, but the network speed is fine otherwise I would suggest this is a fault with the network equipment, and not the network cabling. Possibly a mis-configured computer, or DHCP server. Possibly a switch that is not properly propagating broadcast packets delaying DHCP negotiation.
If the latency is continuous, even after negotiation a faulty cable is more likely (again I would suggest the most likely culprit is the termination).
In the former case advice would be hard to give without more information on your network setup.
In the latter case try a different cable to confirm the fault (for testing purposes this should be a known good cable) and if all is good on that re terminate the suspect link and try it again.