Just to add to the suggestions mentioned. I think someone buying gear whether online or meetups should consider these:
Online (when the seller will ship the gear after a bank deposit or LBC or pera padala etc.)
1. Check the sellers reputation. Many of the sellers here post their previous transactions and you may do a background check on them asking around if the seller is trustworthy. Make sure you have the persons real name, you can go as far as checking his facebook account to identify if he is legit. In this case, pwede mo habulin if na scam ka (e.g. the item is not working properly, missing some parts or much worse, you did not receive the item at all). Ask the Seller about the item. Does it have an issue, was it repaired/ service recently?
2. Plus one on the bank deposit vs lBC or Pera padala. Nothing could be safer.
3. Check out the Item on a music store to make sure you know what you're buying and do some research (what its supposed to do, how it sounds, etc.). Then, Once you've ordered and received the gear, check/test the item immediately upon receiving as some 2nd hand sellers only give you a personal warranty of a few days. Test it thoroughly, twist the knobs to seach for scratchy pots, look for dings and dents, and compare it to what you remember on the music store to make sure it is working the way it should.
Meetups:
1. Same as the first scenario, verify the Identity and Rep of the Seller.
2. Make sure that you TEST the gear to check if its working properly. Ask the seller about the item (issues?, was it service recently?, how old are the tubes?, etc)
3. If its a big transaction, I know the value of money will vary from person to person, but for example, 50K upwards, Bring a Tech with you if you are not familiar with the components of the gear. By all means try to bring a schematic if possible. Have the Tech thoroughly inspect the gear while you are testing it. (This is similar to buying a 2nd hand car where you bring a mechanic with you to check the car you're about to buy.) For that kind of money, you should be sure what you're about to get is original, down to specs and not altered in any way. Unless you know that what you're buying is modded or that's what you're after.
4. Keep your money in the ATM, and just withdraw when both parties have agreed to push thru with the transaction.
I hope this helps.