Well, it has had a BoMar Rear and an aftermarket front sight added to it. That certainly does not mean that it's not worth $300.00 - Will you have a chance to shoot it before you buy it?
Much would depend on if it was radically Home Gunsmithed or not.
If the frame is in factory original condition w/ regard to the frame feed ramp - it would be worth $300 just for the frame.
What you'll want to avoid is buying a sellers FTFunction related 1911 problems. If you can run a function check on it (found in our forum How To & Reference area) and it will hand cycle cartridges then I would buy it in a heartbeat for $300.
Usually if a 1911 has failure to feed problems & the frame feed ramp is intact - then the most common "fix" would be a properly tuned and tensioned extractor which is a very minor issue.
Sadly...there is no way that anybody on this forum - just looking at a PIC of the exterior could tell if that particular 1911 was goofed around with so it's really tough to just say "BUY IT!" - But, $300.00 is a really really good price for a working COLT in good used condition that has just had aftermarket sights added to it.
You should be aware of the fact though that you'll not be able to go back to traditional 1911 sights because the installation of a BoMar modifies the rear dovetail.
Too bad I'm so far away from Texas because I could tell you for certain to "BUY IT - Snap It Up!" after checking it out for a few minutes.
Can you have a good local gunsmith look it over before you purchase it?