1)No repaints. I have a Pogliaghi track bike worth probably 1/8 th what I could get for it if
it were original paint.
2) keep any original parts that you remove, that way if you do decide to sell it you can
easily "restore" it back to the way it came.
3) And this is big: DO NOT REMOVE braze ons, derailleur hangers, etc. to make a fixie out of it.
and conversely don't have braze on's put on a frame that didn't come with them.

Now, as for the "No offence to Treks, but very, very few go for more than $300 on Ebay-pretty much high end walmart prices" I say B.S. Vintage steel treks are an amazing value, and some of them go for
quite a bit (i.e. the $900+ Trek 170 recently seen on ebay). high end walmart prices? Go look at what decent steel bikes sell for on craigslist in some markets. Find a vintage 520 or 720 on ebay and tell me they don't sell or are comprable in price with xmart bikes.

Next question I have is what model trek? and what year?

Marty