Mossberg rifles
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Mossbergs later centerfire rifles were the 800 series. This included the 810 rifles also. Production was ceased in 1978
The 800 series was a short action, and the 810 series was the long action. Therefore, it is possible that the rifle is an 810 Mossberg, because it would need a long action for the .270 cartridge. The designation for the .270 in the 810 series is the 810C or 810CH.
Mossberg also made the RM-7 centerfire rifle from 1978 to 1984. My books indicate a 30-06 chambering and a 7mm Remington Magnum chambering, but not a .270. However, anything is possible.
The RM-7 was not a great success. Mossberg then purchased the remaining stock of Smith and Wesson rifles (made by Sako), in 1985 and sold them until stock ran out. These were the Model 1500 and 1550 series.
If your rifle is one of the 1500 series, you will have a good one. These were built by Sako in Finland, using the Sako L-61 action. Sako rifles have always had a very good reputation for quality and workmanship.
Your best bet is to look at the markings on the barrel and receiver. The model number, and maker, and country of manufacture should be on the rifle.
Without a picture, and better description, it is hard to value an object because of condition. A Mossberg 800 series would be worth $250, but a Mossberg Sako 1500 series would be $350-400. It also depends upon the condition of the bore inside the barrel, any modifications (bubba at work), stock conditions, dings, rust, bluing, and FUNCTIONING. It sounds like you want it for a hunting rifle, rather than a collection piece.
The .270 is a fine calibre for hunting anything in North America, except the big furries that can eat you. The rifle is more than 20 years old, but if kept in a good storage environment, used but not abused, and functions well, then it is acceptable. If it was used as a boat anchor, or stored outside in a barn, then you have to act accordingly.
The Tasco scope is really not worth that much. Tasco made some good ones 20 years ago, but most were the economy type. The optics in the last 20 years has leaped and advanced a lot, and much better scopes are available now at a reasonable price that far outclass the ones of 20 years ago.
As far as making an offer, my answer to that one is "I can not both buy it, and sell it to myself." I usually tell the person that, and tell him that I want to be fair and reasonable, but he must give me an idea of what he wants for the rifle.
The problem with making an offer is that if you are too low, he is insulted. If you go higher than he expected, you may not get the rifle because he figures if you are going to pay that much more for it than he figured it was worth, then it is worth a lot more than what you are willing to pay for it.
Whatever you do, do not brag about getting a rifle at a cheap price. I never tell anyone what I paid for a rifle. If I do get one cheap, and say so, sooner or later the word gets back to the guy who sold it, and he figures you took advantage of him, and that you should have paid more for it, (you crook.)
A last resort is figure out what you want to pay for the rifle, using the advice you got on this forum. Point out, and be aware that parts are very scarce if you break one, and are expensive. Then suggest you write the amount that you are willing to pay on a piece of paper, and he do the same. Compare the prices with him. If he is way out (high), then you can go from there. If he is low, then offer to split the difference. It works most of the time, and about 4 out of 5 times, you will find that your price is the higher one, his is lower, and by splitting the difference, you show what a fair and reasonable guy you are.....he is happy because he gets a bit more, and you get the rifle for a bit less.
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