1.) When you don't know the objective place the computer directly back to the customer, under demands/data etc it often tells you what is expected (eg how much ram he wants, that he has virus, etc).

2.) If a customer requires unspecific PC upgrade for Performance, yet has a low budget (say $150), it is always an upgrade for the RAM.

3.) If a customer says something is wrong with their PC since it doesn't boot, check the interior.
If the fans are intermittently stopping to spin, replace PSU.
If there are graphical glitches, replace GPU.
If you boot and hear 1 beep, replace motherboard. If 3 beeps, replace RAM. 4 beeps, replace CPU.

4.) buy a NAS under equipment. It works like a PC that doesn't need any additional parts nor OS. use this for fixing corrupted HDs. it can't fix burned HDs, nothing can. Sell those HDs and finish the customers job despite red "customer data".

5.) build a cheap computer for yourself! it doesn't need a graphics card nor a good cpu, any super cheap stuff will do.Once you have it running place it somewhere at the back and download all programs (such as antivirus) and drivers. Leave it running at all times, preferably mining bitcoins.
Now whenever someone needs antivirus or new drivers on their PC you just go to computer>lan>your PC and can directly install drivers or programs from there. It is much faster as it skips the download part every time.

6.) Buy 4 USB's and place each Windoor version on them, and one USB for the Ramtest program (use Boot selection button below power button to use). Keep this 4 USB's in your inventory for easy fast installs.

7.) you don't need to restart a computer after virus scan. just turn it off and finish the job.

8.) when a customer has double high-end graphics cards scan both and steal the one with more health. they are worth hundreds if resold to customers or can be used for expensive upgradejobs. (seems to be no longer a valid strategy in full release version.)

9.) do not put cheap items such as DVDs, fans, VRDs, etc on your shelves. Customers might ask for them and buy them but the profit margin is laughable ($2-10) and they actually take away that customer spot, meaning it replaces a higher profit job.

10.) if you have items with low hp (flashing bar) they are pretty much worthless. Customers will not buy them nor accept them as parts in their PCs. treat them just like burned parts and sell them.

11.) do not use the backup program unless you have no money for a NAS, it is strictly worse and slower. and also more unreliable as it only works if the main harddrive with the OS isn't corrupted.

12.) The easiest way to upgrade an OS without losing any data is to buy a new HDD (use cheapest possible) then place that above the other drives, and install the new OS via USB. All drivers and data will remain intact, reducing work required.

13.) Save before moving, as the move will delete all items that aren't in your inventory.